diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 23a24713..fe247e88 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -25,5 +25,4 @@ Until then, please code alike what is there already:
 
 ## Backward Compatibility
 
-Before submission, please remember to check if the code compiles fine on all the supported compilers (especially gcc-9.3 and MSVC are tricky).
-Unfortunately, we cannot add gcc-9.3 to the CI process as it is [not supported by Conan Docker images](https://github.com/conan-io/conan-docker-tools/issues/200).
+Before submission, please remember to check if the code compiles fine on all the supported compilers (gcc-10 and MSVC so far).
diff --git a/conanfile.py b/conanfile.py
index a757b5dd..00fc4e8e 100644
--- a/conanfile.py
+++ b/conanfile.py
@@ -66,8 +66,8 @@ class UnitsConan(ConanFile):
         compiler = self.settings.compiler
         version = Version(self.settings.compiler.version)
         if compiler == "gcc":
-            if version < "9.3":
-                raise ConanInvalidConfiguration("mp-units requires at least g++-9.3")
+            if version < "10.0":
+                raise ConanInvalidConfiguration("mp-units requires at least g++-10")
         elif compiler == "Visual Studio":
             if version < "16":
                 raise ConanInvalidConfiguration("mp-units requires at least MSVC 16")
@@ -88,11 +88,6 @@ class UnitsConan(ConanFile):
     def configure(self):
         self._validate_compiler_settings()
 
-    def requirements(self):
-        if ((self.settings.compiler == "gcc" and Version(self.settings.compiler.version) < "10") or
-            self.settings.compiler == "clang"):
-            self.requires("range-v3/0.11.0")
-
     def build_requirements(self):
         if self._run_tests:
             self.build_requires("catch2/2.13.0")
@@ -123,10 +118,6 @@ class UnitsConan(ConanFile):
                 "-Wno-literal-suffix",
                 "-Wno-non-template-friend",
             ]
-            if version < "10":
-                self.cpp_info.cxxflags.extend([
-                    "-fconcepts"
-                ])
         elif compiler == "Visual Studio":
             self.cpp_info.cxxflags = [
                 "/utf-8",
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 532abc63..2a47137f 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -1,7 +1,7 @@
 # Release notes
 
 - **0.6.0 WIP**
-  - Minimum compiler version supported changed to gcc-9.3
+  - gcc-9 is no longer supported (at least gcc-10 is required)
   - MSVC 16.7 support added
   - linear_algebra updated to 0.7.0/stable
   - fmt updated to 7.0.3
diff --git a/docs/design/quantity.rst b/docs/design/quantity.rst
index 6212886b..a4695c44 100644
--- a/docs/design/quantity.rst
+++ b/docs/design/quantity.rst
@@ -44,7 +44,7 @@ a few additional member types and functions::
 
     template<typename D1, typename U1, typename Rep1, typename D2, typename U2, typename Rep2>
       requires detail::basic_arithmetic<Rep1, Rep2> && (!equivalent_dim<D1, D2>)
-    [[nodiscard]] constexpr Quantity AUTO operator/(const quantity<D1, U1, Rep1>& lhs,
+    [[nodiscard]] constexpr Quantity auto operator/(const quantity<D1, U1, Rep1>& lhs,
                                                     const quantity<D2, U2, Rep2>& rhs);
 
 Additional functions provide the support for operations that result in a
diff --git a/docs/index.rst b/docs/index.rst
index f0697b60..cd430e0d 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -16,7 +16,7 @@ with a permissive `MIT license <https://github.com/mpusz/units/blob/master/LICEN
 .. note::
 
     As this library targets C++23 and extensively uses C++20 features as of now it compiles correctly
-    only with gcc-9.3, MSVC 16.7, and newer.
+    only with gcc-10, MSVC 16.7, and newer.
 
 .. toctree::
     :maxdepth: 2
diff --git a/docs/usage.rst b/docs/usage.rst
index 918a49c7..3d29cd21 100644
--- a/docs/usage.rst
+++ b/docs/usage.rst
@@ -4,7 +4,7 @@ Usage
 .. note::
 
     This library targets C++23 and extensively uses C++20 features that is why, as of now, it compiles correctly
-    only with gcc-9.3, MSVC 16.7, and newer.
+    only with gcc-10, MSVC 16.7, and newer.
 
 Repository Structure and Dependencies
 -------------------------------------
@@ -17,8 +17,6 @@ This repository contains three independent CMake-based projects:
   - when this library will become part of the C++ standard it will have no external dependencies
     but until then it depends on:
 
-    - `range-v3 <https://github.com/ericniebler/range-v3>`_ (only for gcc versions < 10.0) to provide
-      C++20 concepts library definitions.
     - `{fmt} <https://github.com/fmtlib/fmt>`_ to provide text formatting of quantities.
     - `ms-gsl <https://github.com/microsoft/GSL>`_ to verify runtime contracts with `Expects` macro.
 
diff --git a/example/alternative_namespaces/units_str.h b/example/alternative_namespaces/units_str.h
index 3b0bfacd..2dffc459 100644
--- a/example/alternative_namespaces/units_str.h
+++ b/example/alternative_namespaces/units_str.h
@@ -4,7 +4,7 @@
 #include <units/physical/si/prefixes.h>
 #include <units/quantity.h>
 // get at the units text of the quantity, without its numeric value
-inline auto constexpr units_str(const units::Quantity AUTO& q)
+inline auto constexpr units_str(const units::Quantity auto& q)
 {
   typedef std::remove_cvref_t<decltype(q)> qtype;
   return units::detail::unit_text<typename qtype::dimension, typename qtype::unit>();
diff --git a/example/avg_speed.cpp b/example/avg_speed.cpp
index a0c4dbd1..ce7d3782 100644
--- a/example/avg_speed.cpp
+++ b/example/avg_speed.cpp
@@ -44,13 +44,13 @@ fixed_double_si_avg_speed(si::length<si::metre> d,
 }
 
 template<typename U1, typename R1, typename U2, typename R2>
-constexpr Speed AUTO si_avg_speed(si::length<U1, R1> d,
+constexpr Speed auto si_avg_speed(si::length<U1, R1> d,
                                      si::time<U2, R2> t)
 {
   return d / t;
 }
 
-constexpr Speed AUTO avg_speed(Length AUTO d, Time AUTO t)
+constexpr Speed auto avg_speed(Length auto d, Time auto t)
 {
   return d / t;
 }
@@ -68,7 +68,7 @@ void example()
   // SI (int)
   {
     using namespace units::physical::si::literals;
-    constexpr Length AUTO distance = 220q_km;      // constructed from a UDL
+    constexpr Length auto distance = 220q_km;      // constructed from a UDL
     constexpr si::time<si::hour, int> duration(2); // constructed from a value
 
     std::cout << "SI units with 'int' as representation\n";
@@ -82,7 +82,7 @@ void example()
   // SI (double)
   {
     using namespace units::physical::si::literals;
-    constexpr Length AUTO distance = 220.q_km;  // constructed from a UDL
+    constexpr Length auto distance = 220.q_km;  // constructed from a UDL
     constexpr si::time<si::hour> duration(2);   // constructed from a value
 
     std::cout << "\nSI units with 'double' as representation\n";
@@ -98,7 +98,7 @@ void example()
   // Customary Units (int)
   {
     using namespace units::physical::international::literals;
-    constexpr Length AUTO distance = 140q_mi;      // constructed from a UDL
+    constexpr Length auto distance = 140q_mi;      // constructed from a UDL
     constexpr si::time<si::hour, int> duration(2); // constructed from a value
 
     std::cout << "\nUS Customary Units with 'int' as representation\n";
@@ -114,7 +114,7 @@ void example()
   // Customary Units (double)
   {
     using namespace units::physical::international::literals;
-    constexpr Length AUTO distance = 140.q_mi; // constructed from a UDL
+    constexpr Length auto distance = 140.q_mi; // constructed from a UDL
     constexpr si::time<si::hour> duration(2);  // constructed from a value
 
     std::cout << "\nUS Customary Units with 'double' as representation\n";
@@ -132,7 +132,7 @@ void example()
   // CGS (int)
   {
     using namespace units::physical::cgs::literals;
-    constexpr Length AUTO distance = 22'000'000q_cm;  // constructed from a UDL
+    constexpr Length auto distance = 22'000'000q_cm;  // constructed from a UDL
     constexpr cgs::time<si::hour, int> duration(2);   // constructed from a value
 
     std::cout << "\nCGS units with 'int' as representation\n";
@@ -151,7 +151,7 @@ void example()
   // CGS (double)
   {
     using namespace units::physical::cgs::literals;
-    constexpr Length AUTO distance = 22'000'000.q_cm; // constructed from a UDL
+    constexpr Length auto distance = 22'000'000.q_cm; // constructed from a UDL
     constexpr cgs::time<si::hour> duration(2);        // constructed from a value
 
     std::cout << "\nCGS units with 'double' as representation\n";
diff --git a/example/capacitor_time_curve.cpp b/example/capacitor_time_curve.cpp
index cdfa9fc1..51a3e446 100644
--- a/example/capacitor_time_curve.cpp
+++ b/example/capacitor_time_curve.cpp
@@ -41,7 +41,7 @@ int main()
   constexpr auto R = 4.7q_kR;
 
   for (auto t = 0q_ms; t <= 50q_ms; ++t) {
-    const Voltage AUTO Vt = V0 * units::exp(-t / (R * C));
+    const Voltage auto Vt = V0 * units::exp(-t / (R * C));
 
     std::cout << "at " << t << " voltage is ";
 
diff --git a/example/experimental_angle.cpp b/example/experimental_angle.cpp
index d15c75be..620ebe98 100644
--- a/example/experimental_angle.cpp
+++ b/example/experimental_angle.cpp
@@ -34,7 +34,7 @@ int main()
   auto torque = 20.0q_Nm;
   auto energy = 20.0q_J;
 
-  physical::Angle AUTO angle = torque / energy;
+  physical::Angle auto angle = torque / energy;
 
   std::cout << angle << '\n';
 }
diff --git a/example/glide_computer.cpp b/example/glide_computer.cpp
index b35dacec..76f68167 100644
--- a/example/glide_computer.cpp
+++ b/example/glide_computer.cpp
@@ -27,10 +27,7 @@
 #include <units/quantity_point.h>
 #include <array>
 #include <iostream>
-
-#if COMP_MSVC || COMP_GCC >= 10
 #include <compare>
-#endif
 
 // horizontal/vertical vector
 namespace {
@@ -59,10 +56,8 @@ public:
 
   constexpr Q magnitude() const { return magnitude_; }
 
-  template<typename QQ = Q>
   [[nodiscard]] constexpr vector operator-() const
-    requires requires(QQ q) { -q; }
-    // requires requires { -magnitude(); } // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires { -magnitude(); }
   {
     return vector(-magnitude());
   }
@@ -92,15 +87,17 @@ public:
   }
 
   template<typename V>
+    requires (Scalar<V> || Dimensionless<V>)
   [[nodiscard]] friend constexpr auto operator*(const vector& lhs, const V& value)
-    requires (Scalar<V> || Dimensionless<V>) && requires { lhs.magnitude() * value; }
+    requires requires { lhs.magnitude() * value; }
   {
     return vector<Q, D>(lhs.magnitude() * value);
   }
 
   template<typename V>
+    requires (Scalar<V> || Dimensionless<V>)
   [[nodiscard]] friend constexpr auto operator*(const V& value, const vector& rhs)
-    requires (Scalar<V> || Dimensionless<V>) && requires { value * rhs.magnitude(); }
+    requires requires { value * rhs.magnitude(); }
   {
     return vector<Q, D>(value * rhs.magnitude());
   }
@@ -112,8 +109,6 @@ public:
     return lhs.magnitude() / rhs.magnitude();
   }
 
-#if COMP_MSVC || COMP_GCC >= 10
-
   template<typename Q2>
   [[nodiscard]] friend constexpr auto operator<=>(const vector& lhs, const vector<Q2, D>& rhs)
     requires requires { lhs.magnitude() <=> rhs.magnitude(); }
@@ -128,56 +123,8 @@ public:
     return lhs.magnitude() == rhs.magnitude();
   }
 
-#else
-
-  template<typename Q2>
-  [[nodiscard]] friend constexpr auto operator==(const vector& lhs, const vector<Q2, D>& rhs)
-    requires requires { lhs.magnitude() == rhs.magnitude(); }
-  {
-    return lhs.magnitude() == rhs.magnitude();
-  }
-
-  template<typename Q2>
-  [[nodiscard]] friend constexpr auto operator!=(const vector& lhs, const vector<Q2, D>& rhs)
-    requires requires { lhs.magnitude() != rhs.magnitude(); }
-  {
-    return !(lhs == rhs);
-  }
-
-  template<typename Q2>
-  [[nodiscard]] friend constexpr auto operator<(const vector& lhs, const vector<Q2, D>& rhs)
-    requires requires { lhs.magnitude() < rhs.magnitude(); }
-  {
-    return lhs.magnitude() < rhs.magnitude();
-  }
-
-  template<typename Q2>
-  [[nodiscard]] friend constexpr auto operator>(const vector& lhs, const vector<Q2, D>& rhs)
-    requires requires { lhs.magnitude() > rhs.magnitude(); }
-  {
-    return rhs < lhs;
-  }
-
-  template<typename Q2>
-  [[nodiscard]] friend constexpr auto operator<=(const vector& lhs, const vector<Q2, D>& rhs)
-    requires requires { lhs.magnitude() <= rhs.magnitude(); }
-  {
-    return !(rhs < lhs);
-  }
-
-  template<typename Q2>
-  [[nodiscard]] friend constexpr auto operator>=(const vector& lhs, const vector<Q2, D>& rhs)
-    requires requires { lhs.magnitude() >= rhs.magnitude(); }
-  {
-    return !(lhs < rhs);
-  }
-
-#endif
-
-  // template<class CharT, class Traits>
-    // requires Quantity<Q> // TODO gated by gcc-9 (fixed in gcc-10)
-  template<class CharT, class Traits, typename QQ = Q>
-    requires Quantity<QQ>
+  template<class CharT, class Traits>
+    requires Quantity<Q>
   friend std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const vector& v)
   {
     return os << v.magnitude();
@@ -278,7 +225,7 @@ auto get_gliders()
   return gliders;
 }
 
-constexpr Dimensionless AUTO glide_ratio(const glider::polar_point& polar)
+constexpr Dimensionless auto glide_ratio(const glider::polar_point& polar)
 {
   return polar.v / -polar.climb;
 }
diff --git a/example/hello_units.cpp b/example/hello_units.cpp
index 25d20810..a49d12cb 100644
--- a/example/hello_units.cpp
+++ b/example/hello_units.cpp
@@ -27,7 +27,7 @@
 
 using namespace units::physical;
 
-constexpr Speed AUTO avg_speed(Length AUTO d, Time AUTO t)
+constexpr Speed auto avg_speed(Length auto d, Time auto t)
 {
   return d / t;
 }
@@ -35,10 +35,10 @@ constexpr Speed AUTO avg_speed(Length AUTO d, Time AUTO t)
 int main()
 {
   using namespace units::physical::si::literals;
-  Speed AUTO v1 = avg_speed(220q_km, 2q_h);
-  Speed AUTO v2 = avg_speed(si::length<international::mile>(140), si::time<si::hour>(2));
-  Speed AUTO v3 = quantity_cast<si::metre_per_second>(v2);
-  Speed AUTO v4 = quantity_cast<int>(v3);
+  Speed auto v1 = avg_speed(220q_km, 2q_h);
+  Speed auto v2 = avg_speed(si::length<international::mile>(140), si::time<si::hour>(2));
+  Speed auto v3 = quantity_cast<si::metre_per_second>(v2);
+  Speed auto v4 = quantity_cast<int>(v3);
 
   std::cout << v1 << '\n';                             // 110 km/h
   std::cout << fmt::format("{}", v2) << '\n';          // 70 mi/h
diff --git a/example/measurement.cpp b/example/measurement.cpp
index 5691c4ef..1237e7fc 100644
--- a/example/measurement.cpp
+++ b/example/measurement.cpp
@@ -22,11 +22,8 @@
 
 #include <units/physical/si/acceleration.h>
 #include <cmath>
-#include <iostream>
-
-#if COMP_MSVC || COMP_GCC >= 10
 #include <compare>
-#endif
+#include <iostream>
 
 namespace {
 
@@ -105,41 +102,8 @@ public:
     return measurement(val, val * rhs.relative_uncertainty());
   }
 
-#if COMP_MSVC || COMP_GCC >= 10
-
   [[nodiscard]] constexpr auto operator<=>(const measurement&) const = default;
 
-#else
-
-  [[nodiscard]] friend constexpr bool operator==(const measurement& lhs, const measurement& rhs)
-  {
-    return lhs.value() == rhs.value() && lhs.uncertainty() == rhs.uncertainty();
-  }
-
-  [[nodiscard]] friend constexpr bool operator!=(const measurement& lhs, const measurement& rhs)
-  {
-    return !(lhs == rhs);
-  }
-
-  [[nodiscard]] friend constexpr bool operator<(const measurement& lhs, const measurement& rhs)
-  {
-    return lhs.value() == rhs.value() ? lhs.uncertainty() < rhs.uncertainty() : lhs.value() < rhs.value();
-  }
-
-  [[nodiscard]] friend constexpr bool operator>(const measurement& lhs, const measurement& rhs) { return rhs < lhs; }
-
-  [[nodiscard]] friend constexpr bool operator<=(const measurement& lhs, const measurement& rhs)
-  {
-    return !(rhs < lhs);
-  }
-
-  [[nodiscard]] friend constexpr bool operator>=(const measurement& lhs, const measurement& rhs)
-  {
-    return !(lhs < rhs);
-  }
-
-#endif
-
   friend std::ostream& operator<<(std::ostream& os, const measurement& v)
   {
     return os << v.value() << " ± " << v.uncertainty();
@@ -166,7 +130,7 @@ void example()
   const auto a = si::acceleration<si::metre_per_second_sq, measurement<double>>(measurement(9.8, 0.1));
   const auto t = si::time<si::second, measurement<double>>(measurement(1.2, 0.1));
 
-  const Speed AUTO v1 = a * t;
+  const Speed auto v1 = a * t;
   std::cout << a << " * " << t << " = " << v1 << " = " << quantity_cast<si::kilometre_per_hour>(v1) << '\n';
 
   si::length<si::metre, measurement<double>> length(measurement(123., 1.));
diff --git a/example/total_energy.cpp b/example/total_energy.cpp
index 4b15ca92..3ec087ac 100644
--- a/example/total_energy.cpp
+++ b/example/total_energy.cpp
@@ -32,7 +32,7 @@ namespace {
 
 using namespace units::physical;
 
-Energy AUTO total_energy(Momentum AUTO p, Mass AUTO m, Speed AUTO c)
+Energy auto total_energy(Momentum auto p, Mass auto m, Speed auto c)
 {
   return sqrt(pow<2>(p * c) + pow<2>(m * pow<2>(c)));
 }
@@ -42,13 +42,13 @@ void si_example()
   using namespace units::physical::si;
   using GeV = gigaelectronvolt;
 
-  constexpr Speed AUTO c = si2019::speed_of_light<>;
+  constexpr Speed auto c = si2019::speed_of_light<>;
 
   std::cout << "\n*** SI units (c = " << c << ") ***\n";
 
-  const Momentum AUTO p = 4.q_GeV / c;
-  const Mass AUTO m = 3.q_GeV / pow<2>(c);
-  const Energy AUTO E = total_energy(p, m, c);
+  const Momentum auto p = 4.q_GeV / c;
+  const Mass auto m = 3.q_GeV / pow<2>(c);
+  const Energy auto E = total_energy(p, m, c);
 
   std::cout << "[in GeV]\n"
             << "p = " << p << "\n"
@@ -73,10 +73,10 @@ void natural_example()
   using namespace units::physical::natural;
   using GeV = gigaelectronvolt;
 
-  constexpr Speed AUTO c = speed_of_light<>;
+  constexpr Speed auto c = speed_of_light<>;
   const momentum<GeV> p(4);
   const mass<GeV> m(3);
-  const Energy AUTO E = total_energy(p, m, c);
+  const Energy auto E = total_energy(p, m, c);
 
   std::cout << "\n*** Natural units (c = " << c << ") ***\n"
             << "p = " << p << "\n"
diff --git a/example/unknown_dimension.cpp b/example/unknown_dimension.cpp
index f6437b0c..cf90be90 100644
--- a/example/unknown_dimension.cpp
+++ b/example/unknown_dimension.cpp
@@ -26,7 +26,7 @@
 namespace {
 
 template<units::physical::Length D, units::physical::Time T>
-constexpr units::physical::Speed AUTO avg_speed(D d, T t)
+constexpr units::physical::Speed auto avg_speed(D d, T t)
 {
   return d / t;
 }
@@ -36,13 +36,13 @@ void example()
   using namespace units::physical;
   using namespace units::physical::si::literals;
 
-  Length AUTO d1 = 123q_m;
-  Time AUTO t1 = 10q_s;
-  Speed AUTO v1 = avg_speed(d1, t1);
+  Length auto d1 = 123q_m;
+  Time auto t1 = 10q_s;
+  Speed auto v1 = avg_speed(d1, t1);
 
   auto temp1 = v1 * 50q_m;  // produces intermediate unknown dimension with 'unknown_coherent_unit' as its 'coherent_unit'
-  Speed AUTO v2 = temp1 / 100q_m; // back to known dimensions again
-  Length AUTO d2 = v2 * 60q_s;
+  Speed auto v2 = temp1 / 100q_m; // back to known dimensions again
+  Length auto d2 = v2 * 60q_s;
 
   std::cout << "d1 = " << d1 << '\n';
   std::cout << "t1 = " << t1 << '\n';
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 832cc02c..35ad4f77 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -74,17 +74,6 @@ elseif(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
             -Wno-literal-suffix
             -Wno-non-template-friend
     )
-
-    if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 10.0)
-        target_compile_options(mp-units
-            INTERFACE
-                -fconcepts
-        )
-        target_link_libraries(mp-units
-            INTERFACE
-                $<IF:$<TARGET_EXISTS:CONAN_PKG::range-v3>,CONAN_PKG::range-v3,range-v3::range-v3>
-        )
-    endif()
 elseif(CMAKE_CXX_COMPILER_ID STREQUAL "MSVC")
     target_compile_options(mp-units
         INTERFACE
diff --git a/src/include/units/bits/common_quantity.h b/src/include/units/bits/common_quantity.h
index b0530395..20304e83 100644
--- a/src/include/units/bits/common_quantity.h
+++ b/src/include/units/bits/common_quantity.h
@@ -76,16 +76,8 @@ using common_quantity_point = decltype(
 
 }  // namespace units
 
-#if COMP_MSVC || COMP_GCC >= 10
-
 namespace std {
 
-#else
-
-namespace concepts {
-
-#endif
-
 template<units::Quantity Q1, units::Quantity Q2>
   requires units::equivalent_dim<typename Q1::dimension, typename Q2::dimension>
 struct common_type<Q1, Q2> {
diff --git a/src/include/units/bits/external/fixed_string.h b/src/include/units/bits/external/fixed_string.h
index 2f355be3..18adc0bd 100644
--- a/src/include/units/bits/external/fixed_string.h
+++ b/src/include/units/bits/external/fixed_string.h
@@ -26,10 +26,7 @@
 #include <algorithm>
 #include <cstdlib>
 #include <ostream>
-
-#if COMP_MSVC || COMP_GCC >= 10
 #include <compare>
-#endif
 
 namespace units {
 
@@ -76,8 +73,6 @@ struct basic_fixed_string {
     return basic_fixed_string<CharT, N + N2>(txt);
   }
 
-#if COMP_MSVC || COMP_GCC >= 10
-
   [[nodiscard]] constexpr bool operator==(const basic_fixed_string& other) const
   {
     return std::ranges::equal(*this, other);
@@ -92,74 +87,6 @@ struct basic_fixed_string {
     return std::lexicographical_compare_three_way(lhs.begin(), lhs.end(), rhs.begin(), rhs.end());
   }
 
-#else
-
-  [[nodiscard]] constexpr friend bool operator==(const basic_fixed_string& lhs, const basic_fixed_string& rhs) noexcept
-  {
-    for (size_t i = 0; i != lhs.size(); ++i)
-      if (lhs.data_[i] != rhs.data_[i]) return false;
-    return true;
-  }
-
-  [[nodiscard]] constexpr friend bool operator!=(const basic_fixed_string& lhs, const basic_fixed_string& rhs) noexcept
-  {
-    return !(lhs == rhs);
-  }
-
-  template<typename CharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator==(const basic_fixed_string&,
-                                                 const basic_fixed_string<CharT2, N2>&) noexcept
-  {
-    return false;
-  }
-
-  template<typename CharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator!=(const basic_fixed_string&,
-                                                 const basic_fixed_string<CharT2, N2>&) noexcept
-  {
-    return true;
-  }
-
-  template<typename CharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator<(const basic_fixed_string& lhs,
-                                                const basic_fixed_string<CharT2, N2>& rhs) noexcept
-  {
-    using std::begin, std::end;
-    auto first1 = begin(lhs.data_);
-    auto first2 = begin(rhs.data_);
-    const auto last1 = std::prev(end(lhs.data_));  // do not waste time for '\0'
-    const auto last2 = std::prev(end(rhs.data_));
-
-    for (; (first1 != last1) && (first2 != last2); ++first1, (void)++first2) {
-      if (*first1 < *first2) return true;
-      if (*first2 < *first1) return false;
-    }
-    return first1 == last1 && first2 != last2;
-  }
-
-  template<typename CharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator>(const basic_fixed_string& lhs,
-                                                const basic_fixed_string<CharT2, N2>& rhs) noexcept
-  {
-    return rhs < lhs;
-  }
-
-  template<typename CharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator<=(const basic_fixed_string& lhs,
-                                                const basic_fixed_string<CharT2, N2>& rhs) noexcept
-  {
-    return !(rhs < lhs);
-  }
-
-  template<typename CharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator>=(const basic_fixed_string& lhs,
-                                                 const basic_fixed_string<CharT2, N2>& rhs) noexcept
-  {
-    return !(lhs < rhs);
-  }
-
-#endif
-
   template<class Traits>
   friend std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os,
                                                        const basic_fixed_string& txt)
diff --git a/src/include/units/bits/external/hacks.h b/src/include/units/bits/external/hacks.h
index 9831a48f..28f781b9 100644
--- a/src/include/units/bits/external/hacks.h
+++ b/src/include/units/bits/external/hacks.h
@@ -22,7 +22,7 @@
 
 #pragma once
 
-#include <functional>
+#include <concepts>
 
 #if __clang__
 #define COMP_CLANG __clang_major__
@@ -33,29 +33,6 @@
 #define COMP_MSVC _MSC_VER
 #endif
 
-#if COMP_MSVC || COMP_GCC >= 10
-
-#include <concepts>
-
-#else
-
-#include <concepts/concepts.hpp>
-#include <range/v3/range.hpp>
-
-#endif
-
-#if COMP_MSVC || COMP_GCC >= 10 || COMP_CLANG >= 11
-
-#define AUTO auto
-#define SAME_AS(T) std::same_as<T>
-
-#else
-
-#define AUTO
-#define SAME_AS(T) T
-
-#endif
-
 #if COMP_MSVC
 
 #define TYPENAME typename
@@ -66,53 +43,13 @@
 
 #endif
 
+#if COMP_GCC
+
 namespace std {
 
-#if COMP_GCC
-#if COMP_GCC >= 10
-
-  template<class T>
-  concept default_constructible = constructible_from<T>;
-
-#else
-
-  // concepts
-  using concepts::common_reference_with;
-  using concepts::common_with;
-  using concepts::constructible_from;
-  using concepts::convertible_to;
-  using concepts::default_constructible;
-  using concepts::derived_from;
-  using concepts::equality_comparable;
-  using concepts::equality_comparable_with;
-  // using concepts::floating_point;
-  using concepts::integral;
-  using concepts::regular;
-  using concepts::same_as;
-  using concepts::totally_ordered;
-  using concepts::totally_ordered_with;
-
-  namespace ranges {
-
-  using ::ranges::forward_range;
-  using ::ranges::range_value_t;
-
-  }
-
-  // missing in Range-v3
-  template<class T>
-  concept floating_point = std::is_floating_point_v<T>;
-
-  template<class F, class... Args>
-  concept invocable =
-  requires(F&& f, Args&&... args) {
-    std::invoke(std::forward<F>(f), std::forward<Args>(args)...);
-  };
-
-  template<class F, class... Args>
-  concept regular_invocable = invocable<F, Args...>;
-
-#endif
-#endif
+template<class T>
+concept default_constructible = constructible_from<T>;
 
 } // namespace std
+
+#endif
diff --git a/src/include/units/concepts.h b/src/include/units/concepts.h
index 1ec4e064..45cf4c9a 100644
--- a/src/include/units/concepts.h
+++ b/src/include/units/concepts.h
@@ -27,6 +27,7 @@
 #include <units/bits/external/hacks.h>
 #include <units/ratio.h>
 #include <units/bits/external/type_traits.h>
+#include <functional>
 
 namespace units {
 
diff --git a/src/include/units/math.h b/src/include/units/math.h
index f528c1c1..86bcd773 100644
--- a/src/include/units/math.h
+++ b/src/include/units/math.h
@@ -40,7 +40,7 @@ namespace units {
  */
 template<std::intmax_t N, Quantity Q>
   requires(N != 0)
-inline Quantity AUTO pow(const Q& q) noexcept
+inline Quantity auto pow(const Q& q) noexcept
   requires requires { std::pow(q.count(), N); }
 {
   using dim = dimension_pow<typename Q::dimension, N>;
@@ -70,7 +70,7 @@ inline TYPENAME Q::rep pow(const Q&) noexcept
  * @return Quantity The result of computation 
  */
 template<Quantity Q>
-inline Quantity AUTO sqrt(const Q& q) noexcept
+inline Quantity auto sqrt(const Q& q) noexcept
   requires requires { std::sqrt(q.count()); }
 {
   using dim = dimension_sqrt<typename Q::dimension>;
@@ -99,7 +99,7 @@ inline quantity<D, U, Rep> exp(const quantity<D, U, Rep>& q)
  * @return Quantity The absolute value of a provided quantity
  */
 template<Quantity Q>
-inline Quantity AUTO abs(const Q& q) noexcept
+inline Quantity auto abs(const Q& q) noexcept
   requires requires { std::abs(q.count()); }
 {
   return Q(std::abs(q.count()));
@@ -115,7 +115,7 @@ inline Quantity AUTO abs(const Q& q) noexcept
  */
 template<Quantity Q>
   requires requires { std::numeric_limits<typename Q::rep>::epsilon(); }
-constexpr Quantity AUTO epsilon() noexcept
+constexpr Quantity auto epsilon() noexcept
 {
   return Q(std::numeric_limits<typename Q::rep>::epsilon());
 }
diff --git a/src/include/units/quantity.h b/src/include/units/quantity.h
index c7336543..382b245d 100644
--- a/src/include/units/quantity.h
+++ b/src/include/units/quantity.h
@@ -29,11 +29,7 @@
 #include <units/bits/to_string.h>
 #include <units/dimensionless.h>
 #include <units/quantity_cast.h>
-
-#if COMP_MSVC || COMP_GCC >= 10
 #include <compare>
-#endif
-
 #include <ostream>
 
 namespace units {
@@ -90,78 +86,60 @@ public:
 
   [[nodiscard]] constexpr rep count() const noexcept { return value_; }
 
-  template<typename T = Rep>
   [[nodiscard]] static constexpr quantity zero() noexcept
-    requires requires { quantity_values<T>::zero(); }
-  // requires requires { quantity_values<Rep>::zero(); }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires { quantity_values<Rep>::zero(); }
   {
     return quantity(quantity_values<Rep>::zero());
   }
 
-  template<typename T = Rep>
   [[nodiscard]] static constexpr quantity one() noexcept
-    requires requires { quantity_values<T>::one(); }
-  // requires requires { quantity_values<Rep>::one(); }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires { quantity_values<Rep>::one(); }
   {
     return quantity(quantity_values<Rep>::one());
   }
 
-  template<typename T = Rep>
   [[nodiscard]] static constexpr quantity min() noexcept
-    requires requires { quantity_values<T>::min(); }
-  // requires requires { quantity_values<Rep>::min(); }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires { quantity_values<Rep>::min(); }
   {
     return quantity(quantity_values<Rep>::min());
   }
 
-  template<typename T = Rep>
   [[nodiscard]] static constexpr quantity max() noexcept
-    requires requires { quantity_values<T>::max(); }
-  // requires requires { quantity_values<Rep>::max(); }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires { quantity_values<Rep>::max(); }
   {
     return quantity(quantity_values<Rep>::max());
   }
 
   [[nodiscard]] constexpr quantity operator+() const { return *this; }
 
-  template<typename T = Rep>
   [[nodiscard]] constexpr quantity operator-() const
-    requires std::regular_invocable<std::negate<>, T>
-  // requires std::regular_invocable<std::negate<>, rep>  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires std::regular_invocable<std::negate<>, rep>
   {
     return quantity(-count());
   }
 
-  template<typename T = Rep>
   constexpr quantity& operator++()
-    requires requires(T v) { { ++v } -> SAME_AS(T&); }
-  // requires requires(rep v) { { ++v } -> std::same_as<rep&>; }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires(rep v) { { ++v } -> std::same_as<rep&>; }
   {
     ++value_;
     return *this;
   }
 
-  template<typename T = Rep>
   [[nodiscard]] constexpr quantity operator++(int)
-    requires requires(T v) { { v++ } -> SAME_AS(T); }
-  // requires requires(rep v) { { v++ } -> std::same_as<rep>; }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires(rep v) { { v++ } -> std::same_as<rep>; }
   {
     return quantity(value_++);
   }
 
-  template<typename T = Rep>
   constexpr quantity& operator--()
-    requires requires(T v) { { --v } -> SAME_AS(T&); }
-  // requires requires(rep v) { { --v } -> std::same_as<rep&>; }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires(rep v) { { --v } -> std::same_as<rep&>; }
   {
     --value_;
     return *this;
   }
 
-  template<typename T = Rep>
   [[nodiscard]] constexpr quantity operator--(int)
-    requires requires(T v) { { v-- } -> SAME_AS(T); }
-  // requires requires(rep v) { { v-- } -> std::same_as<rep>; }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires(rep v) { { v-- } -> std::same_as<rep>; }
   {
     return quantity(value_--);
   }
@@ -198,22 +176,19 @@ public:
     return *this;
   }
 
-  template<Scalar Value, typename T = Rep>
-  constexpr quantity& operator%=(const Value& rhs)
+  template<Scalar Value>
     requires (!treat_as_floating_point<rep>) &&
-             (!treat_as_floating_point<Value>) &&
-             requires(T v1, Value v2) { { v1 %= v2 } -> SAME_AS(T&); }
-  //  requires(rep v1, Value v2) { { v1 %= v2 } -> SAME_AS(rep&); }  // TODO gated by gcc-9 (fixed in gcc-10)
+             (!treat_as_floating_point<Value>)
+  constexpr quantity& operator%=(const Value& rhs)
+    requires requires(rep v1, Value v2) { { v1 %= v2 } -> std::same_as<rep&>; }
   {
     value_ %= rhs;
     return *this;
   }
 
-  template<typename T = Rep>
   constexpr quantity& operator%=(const quantity& q)
     requires (!treat_as_floating_point<rep>) &&
-             requires(T v1, T v2) { { v1 %= v2 } -> SAME_AS(T&); }
-  // requires(rep v1, rep v2) { { v1 %= v2 } -> std::same_as<rep&>; }  // TODO gated by gcc-9 (fixed in gcc-10)
+             requires(rep v1, rep v2) { { v1 %= v2 } -> std::same_as<rep&>; }
   {
     value_ %= q.count();
     return *this;
@@ -229,8 +204,8 @@ public:
   }
 
   template<typename U2, typename Rep2>
-  [[nodiscard]] friend constexpr Quantity AUTO operator+(const quantity& lhs, const quantity<D, U2, Rep2>& rhs)
     requires std::regular_invocable<std::plus<>, Rep, Rep2>
+  [[nodiscard]] friend constexpr Quantity auto operator+(const quantity& lhs, const quantity<D, U2, Rep2>& rhs)
   {
     using common_rep = decltype(lhs.count() + rhs.count());
     using ret = common_quantity<quantity, quantity<D, U2, Rep2>, common_rep>;
@@ -244,8 +219,8 @@ public:
   }
 
   template<typename U2, typename Rep2>
-  [[nodiscard]] friend constexpr Quantity AUTO operator-(const quantity& lhs, const quantity<D, U2, Rep2>& rhs)
     requires std::regular_invocable<std::minus<>, Rep, Rep2>
+  [[nodiscard]] friend constexpr Quantity auto operator-(const quantity& lhs, const quantity<D, U2, Rep2>& rhs)
   {
     using common_rep = decltype(lhs.count() - rhs.count());
     using ret = common_quantity<quantity, quantity<D, U2, Rep2>, common_rep>;
@@ -253,8 +228,8 @@ public:
   }
 
   template<Scalar Value>
-  [[nodiscard]] friend constexpr Quantity AUTO operator*(const quantity& q, const Value& v)
     requires std::regular_invocable<std::multiplies<>, Rep, Value>
+  [[nodiscard]] friend constexpr Quantity auto operator*(const quantity& q, const Value& v)
   {
     using common_rep = decltype(q.count() * v);
     using ret = quantity<D, U, common_rep>;
@@ -262,15 +237,15 @@ public:
   }
 
   template<Scalar Value>
-  [[nodiscard]] friend constexpr Quantity AUTO operator*(const Value& v, const quantity& q)
     requires std::regular_invocable<std::multiplies<>, Value, Rep>
+  [[nodiscard]] friend constexpr Quantity auto operator*(const Value& v, const quantity& q)
   {
     return q * v;
   }
 
   template<typename D2, typename U2, typename Rep2>
-  [[nodiscard]] friend constexpr Quantity AUTO operator*(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
     requires std::regular_invocable<std::multiplies<>, Rep, Rep2>
+  [[nodiscard]] friend constexpr Quantity auto operator*(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
   {
     using dim = dimension_multiply<D, D2>;
     using ret_unit = downcast_unit<dim, (U::ratio / dimension_unit<D>::ratio) * (U2::ratio / dimension_unit<D2>::ratio) * dimension_unit<dim>::ratio>;
@@ -280,8 +255,8 @@ public:
   }
 
   template<Scalar Value>
-  [[nodiscard]] friend constexpr Quantity AUTO operator/(const Value& v, const quantity& q)
     requires std::regular_invocable<std::divides<>, Value, Rep>
+  [[nodiscard]] friend constexpr Quantity auto operator/(const Value& v, const quantity& q)
   {
     Expects(q.count() != 0);
 
@@ -293,8 +268,8 @@ public:
   }
 
   template<Scalar Value>
-  [[nodiscard]] friend constexpr Quantity AUTO operator/(const quantity& q, const Value& v)
     requires std::regular_invocable<std::divides<>, Rep, Value>
+  [[nodiscard]] friend constexpr Quantity auto operator/(const quantity& q, const Value& v)
   {
     Expects(v != Value{0});
 
@@ -304,8 +279,8 @@ public:
   }
 
   template<typename D2, typename U2, typename Rep2>
-  [[nodiscard]] friend constexpr Quantity AUTO operator/(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
     requires std::regular_invocable<std::divides<>, Rep, Rep2>
+  [[nodiscard]] friend constexpr Quantity auto operator/(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
   {
     Expects(rhs.count() != 0);
 
@@ -317,10 +292,10 @@ public:
   }
 
   template<Scalar Value>
-  [[nodiscard]] friend constexpr Quantity AUTO operator%(const quantity& q, const Value& v)
     requires (!treat_as_floating_point<Rep>) &&
             (!treat_as_floating_point<Value>) &&
             std::regular_invocable<std::modulus<>, Rep, Value>
+  [[nodiscard]] friend constexpr Quantity auto operator%(const quantity& q, const Value& v)
   {
     using common_rep = decltype(q.count() % v);
     using ret = quantity<D, U, common_rep>;
@@ -328,90 +303,34 @@ public:
   }
 
   template<typename U2, typename Rep2>
-  [[nodiscard]] friend constexpr Quantity AUTO operator%(const quantity& lhs, const quantity<D, U2, Rep2>& rhs)
     requires (!treat_as_floating_point<Rep>) &&
             (!treat_as_floating_point<Rep2>) &&
             std::regular_invocable<std::modulus<>, Rep, Rep2>
+  [[nodiscard]] friend constexpr Quantity auto operator%(const quantity& lhs, const quantity<D, U2, Rep2>& rhs)
   {
     using common_rep = decltype(lhs.count() % rhs.count());
     using ret = common_quantity<quantity, quantity<D, U2, Rep2>, common_rep>;
     return ret(ret(lhs).count() % ret(rhs).count());
   }
 
-#if COMP_MSVC || COMP_GCC >= 10
-
   template<typename D2, typename U2, typename Rep2>
-  [[nodiscard]] friend constexpr auto operator<=>(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
     requires equivalent_dim<D, D2> &&
              std::three_way_comparable_with<Rep, Rep2>
+  [[nodiscard]] friend constexpr auto operator<=>(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
   {
     using cq = common_quantity<quantity, quantity<D2, U2, Rep2>>;
     return cq(lhs).count() <=> cq(rhs).count();
   }
 
   template<typename D2, typename U2, typename Rep2>
-  [[nodiscard]] friend constexpr bool operator==(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
     requires equivalent_dim<D, D2> &&
              std::equality_comparable_with<Rep, Rep2>
+  [[nodiscard]] friend constexpr bool operator==(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
   {
     using cq = common_quantity<quantity, quantity<D2, U2, Rep2>>;
     return cq(lhs).count() == cq(rhs).count();
   }
 
-#else
-
-  template<typename D2, typename U2, typename Rep2>
-  [[nodiscard]] friend constexpr bool operator==(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
-    requires equivalent_dim<D, D2> &&
-             std::equality_comparable_with<Rep, Rep2>
-  {
-    using cq = common_quantity<quantity, quantity<D2, U2, Rep2>>;
-    return cq(lhs).count() == cq(rhs).count();
-  }
-
-  template<typename D2, typename U2, typename Rep2>
-  [[nodiscard]] friend constexpr bool operator!=(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
-    requires equivalent_dim<D, D2> &&
-             std::equality_comparable_with<Rep, Rep2>
-  {
-    return !(lhs == rhs);
-  }
-
-  template<typename D2, typename U2, typename Rep2>
-  [[nodiscard]] friend constexpr bool operator<(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
-    requires equivalent_dim<D, D2> &&
-             std::totally_ordered_with<Rep, Rep2>
-  {
-    using cq = common_quantity<quantity, quantity<D2, U2, Rep2>>;
-    return cq(lhs).count() < cq(rhs).count();
-  }
-
-  template<typename D2, typename U2, typename Rep2>
-  [[nodiscard]] friend constexpr bool operator<=(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
-    requires equivalent_dim<D, D2> &&
-             std::totally_ordered_with<Rep, Rep2>
-  {
-    return !(rhs < lhs);
-  }
-
-  template<typename D2, typename U2, typename Rep2>
-  [[nodiscard]] friend constexpr bool operator>(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
-    requires equivalent_dim<D, D2> &&
-             std::totally_ordered_with<Rep, Rep2>
-  {
-    return rhs < lhs;
-  }
-
-  template<typename D2, typename U2, typename Rep2>
-  [[nodiscard]] friend constexpr bool operator>=(const quantity& lhs, const quantity<D2, U2, Rep2>& rhs)
-    requires equivalent_dim<D, D2> &&
-             std::totally_ordered_with<Rep, Rep2>
-  {
-    return !(lhs < rhs);
-  }
-
-#endif
-
   template<class CharT, class Traits>
   friend std::basic_ostream<CharT, Traits>& operator<<(std::basic_ostream<CharT, Traits>& os, const quantity& q)
   {
diff --git a/src/include/units/quantity_cast.h b/src/include/units/quantity_cast.h
index 2f51af6b..d695b671 100644
--- a/src/include/units/quantity_cast.h
+++ b/src/include/units/quantity_cast.h
@@ -313,8 +313,8 @@ constexpr ratio cast_ratio(const Q1& from, const Q2& to)
  * @tparam To a target quantity type to cast to
  */
 template<Quantity To, typename D, typename U, typename Rep>
-[[nodiscard]] constexpr auto quantity_cast(const quantity<D, U, Rep>& q)
   requires QuantityOf<To, D>
+[[nodiscard]] constexpr auto quantity_cast(const quantity<D, U, Rep>& q)
 {
   using c_ratio = std::integral_constant<ratio, detail::cast_ratio(quantity<D, U, Rep>(), To())>;
   using c_rep = std::common_type_t<typename To::rep, Rep>;
@@ -337,8 +337,8 @@ template<Quantity To, typename D, typename U, typename Rep>
  * @tparam ToD a dimension type to use for a target quantity
  */
 template<Dimension ToD, typename D, typename U, typename Rep>
-[[nodiscard]] constexpr auto quantity_cast(const quantity<D, U, Rep>& q)
   requires equivalent_dim<ToD, D>
+[[nodiscard]] constexpr auto quantity_cast(const quantity<D, U, Rep>& q)
 {
   return quantity_cast<quantity<ToD, dimension_unit<ToD>, Rep>>(q);
 }
@@ -356,8 +356,8 @@ template<Dimension ToD, typename D, typename U, typename Rep>
  * @tparam ToU a unit type to use for a target quantity
  */
 template<Unit ToU, typename D, typename U, typename Rep>
-[[nodiscard]] constexpr auto quantity_cast(const quantity<D, U, Rep>& q)
   requires UnitOf<ToU, D>
+[[nodiscard]] constexpr auto quantity_cast(const quantity<D, U, Rep>& q)
 {
   return quantity_cast<quantity<D, ToU, Rep>>(q);
 }
@@ -397,9 +397,9 @@ template<Scalar ToRep, typename D, typename U, typename Rep>
  * @tparam CastSpec a target quantity point type to cast to or anything that works for quantity_cast
  */
 template<typename CastSpec, typename D, typename U, typename Rep>
-[[nodiscard]] constexpr auto quantity_point_cast(const quantity_point<D, U, Rep>& qp)
   requires is_specialization_of<CastSpec, quantity_point> ||
            requires(quantity<D, U, Rep> q) { quantity_cast<CastSpec>(q); }
+[[nodiscard]] constexpr auto quantity_point_cast(const quantity_point<D, U, Rep>& qp)
 {
   if constexpr (is_specialization_of<CastSpec, quantity_point>)
     return quantity_point(quantity_cast<typename CastSpec::quantity_type>(qp.relative()));
diff --git a/src/include/units/quantity_point.h b/src/include/units/quantity_point.h
index 863851ba..3777ef32 100644
--- a/src/include/units/quantity_point.h
+++ b/src/include/units/quantity_point.h
@@ -24,10 +24,7 @@
 #pragma once
 
 #include <units/quantity.h>
-
-#if COMP_MSVC || COMP_GCC >= 10
 #include <compare>
-#endif
 
 namespace units {
 
@@ -69,69 +66,53 @@ public:
 
   [[nodiscard]] constexpr quantity_type relative() const noexcept { return q_; }
 
-  template<typename Q = quantity_type>
   [[nodiscard]] static constexpr quantity_point min() noexcept
-    requires requires { Q::min(); }
-  // requires requires { quantity_type::min(); }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires { quantity_type::min(); }
   {
     return quantity_point(quantity_type::min());
   }
 
-  template<typename Q = quantity_type>
   [[nodiscard]] static constexpr quantity_point max() noexcept
-    requires requires { Q::max(); }
-  // requires requires { quantity_type::max(); }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires { quantity_type::max(); }
   {
     return quantity_point(quantity_type::max());
   }
 
-  template<typename Q = quantity_type>
-    requires requires(Q q) { ++q; }
   constexpr quantity_point& operator++()
-  // requires requires(quantity_type q) { ++q; }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires(quantity_type q) { ++q; }
   {
     ++q_;
     return *this;
   }
 
-  template<typename Q = quantity_type>
   [[nodiscard]] constexpr quantity_point operator++(int)
-    requires requires(Q q) { q++; }
-  // requires requires(quantity_type q) { q++; }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires(quantity_type q) { q++; }
   {
     return quantity_point(q_++);
   }
 
-  template<typename Q = quantity_type>
-    requires requires(Q q) { --q; }
   constexpr quantity_point& operator--()
-  // requires requires(quantity_type q) { --q; }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires(quantity_type q) { --q; }
   {
     --q_;
     return *this;
   }
 
-  template<typename Q = quantity_type>
   [[nodiscard]] constexpr quantity_point operator--(int)
-    requires requires(Q q) { q--; }
-  // requires requires(quantity_type q) { q--; }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires(quantity_type q) { q--; }
   {
     return quantity_point(q_--);
   }
 
-  template<typename Q = quantity_type>
-    requires requires(Q q1, Q q2) { q1 += q2; }
   constexpr quantity_point& operator+=(const quantity_type& q)
-  // requires requires(quantity_type q) { q += q; }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires(quantity_type q) { q += q; }
   {
     q_ += q;
     return *this;
   }
 
-  template<typename Q = quantity_type>
-    requires requires(Q q1, Q q2) { q1 -= q2; }
   constexpr quantity_point& operator-=(const quantity_type& q)
-  // requires requires(quantity_type q) { q1 -= q2; }  // TODO gated by gcc-9 (fixed in gcc-10)
+    requires requires(quantity_type q1, quantity_type q2) { q1 -= q2; }
   {
     q_ -= q;
     return *this;
@@ -139,100 +120,58 @@ public:
 
   // Hidden Friends
   // Below friend functions are to be found via argument-dependent lookup only
-#if COMP_MSVC || COMP_GCC >= 10
+
+  template<Quantity Q>
+  [[nodiscard]] friend constexpr QuantityPoint auto operator+(const quantity_point& lhs, const Q& rhs)
+    requires requires { lhs.relative() + rhs; }
+  {
+    const auto q = lhs.relative() + rhs;
+    using q_type = decltype(q);
+    return quantity_point<typename q_type::dimension, typename q_type::unit, typename q_type::rep>(q);
+  }
+
+  template<Quantity Q>
+  [[nodiscard]] friend constexpr QuantityPoint auto operator+(const Q& lhs, const quantity_point& rhs)
+    requires requires { rhs + lhs; }
+  {
+    return rhs + lhs;
+  }
+
+  template<Quantity Q>
+  [[nodiscard]] friend constexpr QuantityPoint auto operator-(const quantity_point& lhs, const Q& rhs)
+    requires requires { lhs.relative() - rhs; }
+  {
+    const auto q = lhs.relative() - rhs;
+    using q_type = decltype(q);
+    return quantity_point<typename q_type::dimension, typename q_type::unit, typename q_type::rep>(q);
+  }
+
+  template<QuantityPoint QP>
+  [[nodiscard]] friend constexpr Quantity auto operator-(const quantity_point& lhs, const QP& rhs)
+    requires requires { lhs.relative() - rhs.relative(); }
+  {
+    return lhs.relative() - rhs.relative();
+  }
 
   template<QuantityPoint QP>
-  [[nodiscard]] friend constexpr auto operator<=>(const quantity_point& lhs, const QP& rhs)
     requires std::three_way_comparable_with<quantity_type, typename QP::quantity_type>
+  [[nodiscard]] friend constexpr auto operator<=>(const quantity_point& lhs, const QP& rhs)
   {
     return lhs.relative() <=> rhs.relative();
   }
 
   template<QuantityPoint QP>
-  [[nodiscard]] friend constexpr bool operator==(const quantity_point& lhs, const QP& rhs)
     requires std::equality_comparable_with<quantity_type, typename QP::quantity_type>
+  [[nodiscard]] friend constexpr bool operator==(const quantity_point& lhs, const QP& rhs)
   {
     return lhs.relative() == rhs.relative();
   }
 
-#else
-
-  template<QuantityPoint QP>
-  [[nodiscard]] friend constexpr bool operator==(const quantity_point& lhs, const QP& rhs)
-    requires std::equality_comparable_with<quantity_type, typename QP::quantity_type>
-  {
-    return lhs.relative() == rhs.relative();
-  }
-
-  template<QuantityPoint QP>
-  [[nodiscard]] friend constexpr bool operator!=(const quantity_point& lhs, const QP& rhs)
-    requires std::equality_comparable_with<quantity_type, typename QP::quantity_type>
-  {
-    return !(lhs == rhs);
-  }
-
-  template<QuantityPoint QP>
-  [[nodiscard]] friend constexpr bool operator<(const quantity_point& lhs, const QP& rhs)
-    requires std::totally_ordered_with<quantity_type, typename QP::quantity_type>
-  {
-    return lhs.relative() < rhs.relative();
-  }
-
-  template<QuantityPoint QP>
-  [[nodiscard]] friend constexpr bool operator<=(const quantity_point& lhs, const QP& rhs)
-    requires std::totally_ordered_with<quantity_type, typename QP::quantity_type>
-  {
-    return !(rhs < lhs);
-  }
-
-  template<QuantityPoint QP>
-  [[nodiscard]] friend constexpr bool operator>(const quantity_point& lhs, const QP& rhs)
-    requires std::totally_ordered_with<quantity_type, typename QP::quantity_type>
-  {
-    return rhs < lhs;
-  }
-
-  template<QuantityPoint QP>
-  [[nodiscard]] friend constexpr bool operator>=(const quantity_point& lhs, const QP& rhs)
-    requires std::totally_ordered_with<quantity_type, typename QP::quantity_type>
-  {
-    return !(lhs < rhs);
-  }
-
-#endif
 };
 
 template<typename D, typename U, typename Rep>
 quantity_point(quantity<D, U, Rep>) -> quantity_point<D, U, Rep>;
 
-template<QuantityPoint QP, Quantity Q>
-[[nodiscard]] constexpr QuantityPoint AUTO operator+(const QP& lhs, const Q& rhs)
-  requires requires { lhs.relative() + rhs; }
-{
-  return quantity_point(lhs.relative() + rhs);
-}
-
-template<Quantity Q, QuantityPoint QP>
-[[nodiscard]] constexpr QuantityPoint AUTO operator+(const Q& lhs, const QP& rhs)
-  requires requires { rhs + lhs; }
-{
-  return rhs + lhs;
-}
-
-template<QuantityPoint QP, Quantity Q>
-[[nodiscard]] constexpr QuantityPoint AUTO operator-(const QP& lhs, const Q& rhs)
-  requires requires { lhs.relative() - rhs; }
-{
-  return quantity_point(lhs.relative() - rhs);
-}
-
-template<QuantityPoint QP1, QuantityPoint QP2>
-[[nodiscard]] constexpr Quantity AUTO operator-(const QP1& lhs, const QP2& rhs)
-  requires requires { lhs.relative() - rhs.relative(); }
-{
-  return lhs.relative() - rhs.relative();
-}
-
 namespace detail {
 
 template<typename D, typename U, typename Rep>
diff --git a/src/include/units/ratio.h b/src/include/units/ratio.h
index c21f196c..ff98b0bf 100644
--- a/src/include/units/ratio.h
+++ b/src/include/units/ratio.h
@@ -55,24 +55,8 @@ struct ratio {
     detail::normalize(num, den, exp);
   }
 
-#if COMP_MSVC || COMP_GCC >= 10
-
   [[nodiscard]] friend constexpr bool operator==(const ratio&, const ratio&) = default;
 
-#else
-
-  [[nodiscard]] friend constexpr bool operator==(const ratio& lhs, const ratio& rhs)
-  {
-    return lhs.num == rhs.num && lhs.den == rhs.den && lhs.exp == rhs.exp;
-  }
-
-  [[nodiscard]] friend constexpr bool operator!=(const ratio& lhs, const ratio& rhs)
-  {
-    return !(lhs == rhs);
-  }
-
-#endif
-
   [[nodiscard]] friend constexpr ratio operator*(const ratio& lhs, const ratio& rhs)
   {
     const std::intmax_t gcd1 = std::gcd(lhs.num, rhs.den);
diff --git a/src/include/units/symbol_text.h b/src/include/units/symbol_text.h
index 131979ac..f38ee6f2 100644
--- a/src/include/units/symbol_text.h
+++ b/src/include/units/symbol_text.h
@@ -25,10 +25,7 @@
 #include <units/bits/external/fixed_string.h>
 #include <units/bits/external/hacks.h>
 #include <gsl/gsl_assert>
-
-#if COMP_MSVC || COMP_GCC >= 10
 #include <compare>
-#endif
 
 namespace units {
 
@@ -125,8 +122,6 @@ struct basic_symbol_text {
     return basic_symbol_text<StandardCharT, 1, 1>(lhs) + rhs;
   }
 
-#if COMP_MSVC || COMP_GCC >= 10
-
   template<typename StandardCharT2, std::size_t N2, std::size_t M2>
   [[nodiscard]] friend constexpr auto operator<=>(const basic_symbol_text& lhs,
                                                   const basic_symbol_text<StandardCharT2, N2, M2>& rhs) noexcept
@@ -141,217 +136,6 @@ struct basic_symbol_text {
   {
     return lhs.standard() == rhs.standard() && lhs.ascii() == rhs.ascii();
   }
-
-#else
-
-  // I did not update the below operators with comparing ASCII as this code is going to be deleted soon anyway...
-
-  template<typename StandardCharT2, std::size_t N2, std::size_t M2>
-  [[nodiscard]] constexpr friend bool operator==(const basic_symbol_text& lhs,
-                                                 const basic_symbol_text<StandardCharT2, N2, M2>& rhs) noexcept
-  {
-    return lhs.standard() == rhs.standard();
-  }
-
-  template<typename StandardCharT2, std::size_t N2, std::size_t M2>
-  [[nodiscard]] constexpr friend bool operator!=(const basic_symbol_text& lhs,
-                                                 const basic_symbol_text<StandardCharT2, N2, M2>& rhs) noexcept
-  {
-    return !(lhs == rhs);
-  }
-
-  [[nodiscard]] constexpr friend bool operator==(const basic_symbol_text& lhs,
-                                                 const basic_fixed_string<StandardCharT, N>& rhs) noexcept
-  {
-    return lhs.standard() == rhs;
-  }
-
-  [[nodiscard]] constexpr friend bool operator!=(const basic_symbol_text& lhs,
-                                                 const basic_fixed_string<StandardCharT, N>& rhs) noexcept
-  {
-    return !(lhs == rhs);
-  }
-  
-  template<typename StandardCharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator==(const basic_symbol_text&,
-                                                 const basic_fixed_string<StandardCharT2, N2>&) noexcept
-  {
-    return false;
-  }
-
-  template<typename StandardCharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator!=(const basic_symbol_text&,
-                                                 const basic_fixed_string<StandardCharT2, N2>&) noexcept
-  {
-    return true;
-  }
-  
-  [[nodiscard]] constexpr friend bool operator==(const basic_symbol_text& lhs,
-                                                 const StandardCharT (&rhs)[N + 1]) noexcept
-  {
-    return lhs.standard() == rhs;
-  }
-
-  [[nodiscard]] constexpr friend bool operator!=(const basic_symbol_text& lhs,
-                                                 const StandardCharT (&rhs)[N + 1]) noexcept
-  {
-    return !(lhs == rhs);
-  }
-  
-  template<typename StandardCharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator==(const basic_symbol_text&,
-                                                 const StandardCharT2 (&)[N2 + 1]) noexcept
-  {
-    return false;
-  }
-
-  template<typename StandardCharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator!=(const basic_symbol_text&,
-                                                 const StandardCharT2 (&)[N2 + 1]) noexcept
-  {
-    return true;
-  }
-
-  [[nodiscard]] constexpr friend bool operator==(const basic_symbol_text& lhs,
-                                                 StandardCharT rhs) noexcept
-  {
-    return lhs.standard() == rhs;
-  }
-
-  [[nodiscard]] constexpr friend bool operator!=(const basic_symbol_text& lhs,
-                                                 StandardCharT rhs) noexcept
-  {
-    return !(lhs == rhs);
-  }
-
-  template<typename StandardCharT2>
-  [[nodiscard]] constexpr friend bool operator==(const basic_symbol_text&,
-                                                 StandardCharT2) noexcept
-  {
-    return false;
-  }
-
-  template<typename StandardCharT2>
-  [[nodiscard]] constexpr friend bool operator!=(const basic_symbol_text&,
-                                                 StandardCharT2) noexcept
-  {
-    return true;
-  }
-
-  template<typename StandardCharT2, std::size_t N2, std::size_t M2>
-  [[nodiscard]] constexpr friend bool operator<(const basic_symbol_text& lhs,
-                                                const basic_symbol_text<StandardCharT2, N2, M2>& rhs) noexcept
-  {
-     return lhs.standard() < rhs.standard();
-  }
-
-  template<typename StandardCharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator<(const basic_symbol_text& lhs,
-                                                const basic_fixed_string<StandardCharT2, N2>& rhs) noexcept
-  {
-    return lhs.standard() < rhs;
-  }
-
-  template<typename StandardCharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator<(const basic_symbol_text& lhs,
-                                                const StandardCharT2 (&rhs)[N2]) noexcept
-  {
-    return lhs.standard() < basic_fixed_string(rhs);
-  }
-
-  template<typename StandardCharT2>
-  [[nodiscard]] constexpr friend bool operator<(const basic_symbol_text& lhs,
-                                                StandardCharT2 rhs) noexcept
-  {
-    return lhs.standard() < basic_fixed_string(rhs);
-  }
-
-  template<typename StandardCharT2, std::size_t N2, std::size_t M2>
-  [[nodiscard]] constexpr friend bool operator>(const basic_symbol_text& lhs,
-                                                const basic_symbol_text<StandardCharT2, N2, M2>& rhs) noexcept
-  {
-    return rhs < lhs;
-  }
-
-  template<typename StandardCharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator>(const basic_symbol_text& lhs,
-        const basic_fixed_string<StandardCharT2, N2>& rhs) noexcept
-  {
-    return rhs < lhs;
-  }
-
-  template<typename StandardCharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator>(const basic_symbol_text& lhs,
-        const StandardCharT2 (&rhs)[N2]) noexcept
-  {
-    return rhs < lhs;
-  }
-
-  template<typename StandardCharT2>
-  [[nodiscard]] constexpr friend bool operator>(const basic_symbol_text& lhs,
-                                                StandardCharT2 rhs) noexcept
-  {
-    return rhs < lhs;
-  }
-
-  template<typename StandardCharT2, std::size_t N2, std::size_t M2>
-  [[nodiscard]] constexpr friend bool operator<=(const basic_symbol_text& lhs,
-                                                 const basic_symbol_text<StandardCharT2, N2, M2>& rhs) noexcept
-  {
-    return !(rhs < lhs);
-  }
-
-  template<typename StandardCharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator<=(const basic_symbol_text& lhs,
-                                                 const basic_fixed_string<StandardCharT2, N2>& rhs) noexcept
-  {
-    return !(rhs < lhs);
-  }
-
-  template<typename StandardCharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator<=(const basic_symbol_text& lhs,
-                                                 const StandardCharT2 (&rhs)[N2]) noexcept
-  {
-    return !(rhs < lhs);
-  }
-
-  template<typename StandardCharT2>
-  [[nodiscard]] constexpr friend bool operator<=(const basic_symbol_text& lhs,
-                                                 StandardCharT2 rhs) noexcept
-  {
-    return !(rhs < lhs);
-  }
-
-  template<typename StandardCharT2, std::size_t N2, std::size_t M2>
-  [[nodiscard]] constexpr friend bool operator>=(const basic_symbol_text& lhs,
-                                                 const basic_symbol_text<StandardCharT2, N2, M2>& rhs) noexcept
-  {
-    return !(lhs < rhs);
-  }
-
-  template<typename StandardCharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator>=(const basic_symbol_text& lhs,
-                                                 const basic_fixed_string<StandardCharT2, N2>& rhs) noexcept
-  {
-    return !(lhs < rhs);
-  }
-
-  template<typename StandardCharT2, std::size_t N2>
-  [[nodiscard]] constexpr friend bool operator>=(const basic_symbol_text& lhs,
-                                                 const StandardCharT2 (&rhs)[N2]) noexcept
-  {
-    return !(lhs < rhs);
-  }
-
-  template<typename StandardCharT2>
-  [[nodiscard]] constexpr friend bool operator>=(const basic_symbol_text& lhs,
-                                                 StandardCharT2 rhs) noexcept
-  {
-    return !(lhs < rhs);
-  }
-
-#endif
-
 };
 
 basic_symbol_text(char) -> basic_symbol_text<char, 1, 1>;
diff --git a/test_package/test_package.cpp b/test_package/test_package.cpp
index ba5d8742..86df020c 100644
--- a/test_package/test_package.cpp
+++ b/test_package/test_package.cpp
@@ -25,7 +25,7 @@
 
 using namespace units::physical;
 
-constexpr Speed AUTO avg_speed(Length AUTO d, Time AUTO t)
+constexpr Speed auto avg_speed(Length auto d, Time auto t)
 {
   return d / t;
 }