diff --git a/doc/smart_ptr/intrusive_ref_counter.adoc b/doc/smart_ptr/intrusive_ref_counter.adoc
index 091f9cd..1d33300 100644
--- a/doc/smart_ptr/intrusive_ref_counter.adoc
+++ b/doc/smart_ptr/intrusive_ref_counter.adoc
@@ -60,6 +60,14 @@ namespace boost {
   protected:
     ~intrusive_ref_counter() = default;
   };
+
+  template<class Derived, class CounterPolicy>
+    void intrusive_ptr_add_ref(
+      const intrusive_ref_counter<Derived, CounterPolicy>* p) noexcept;
+
+  template<class Derived, class CounterPolicy>
+    void intrusive_ptr_release(
+      const intrusive_ref_counter<Derived, CounterPolicy>* p) noexcept;
 }
 ```
 
@@ -99,7 +107,7 @@ intrusive_ref_counter& operator=(const intrusive_ref_counter& v) noexcept;
 ```
 ::
 Effects::: Does nothing, reference counter is not modified.
-
+y
 ### use_count
 
 ```
@@ -109,3 +117,26 @@ unsigned int use_count() const noexcept;
 Returns::: The current value of the reference counter.
 
 NOTE: The returned value may not be actual in multi-threaded applications.
+
+## Free Functions
+
+### intrusive_ptr_add_ref
+
+```
+template<class Derived, class CounterPolicy>
+  void intrusive_ptr_add_ref(
+    const intrusive_ref_counter<Derived, CounterPolicy>* p) noexcept;
+```
+::
+Effects::: Increments the reference counter.
+
+### intrusive_ptr_release
+
+```
+template<class Derived, class CounterPolicy>
+  void intrusive_ptr_release(
+    const intrusive_ref_counter<Derived, CounterPolicy>* p) noexcept;
+```
+::
+Effects::: Decrements the reference counter. If the reference counter reaches
+0, calls `delete static_cast<const Derived*>(p)`.