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+[alg.count]
+
+# 26 Algorithms library [[algorithms]](./#algorithms)
+
+## 26.6 Non-modifying sequence operations [[alg.nonmodifying]](alg.nonmodifying#alg.count)
+
+### 26.6.11 Count [alg.count]
+
+[ð](#lib:count)
+
+`template<class InputIterator, class T = iterator_traits<InputIterator>::value_type>
+  constexpr typename iterator_traits<InputIterator>::difference_type
+    count(InputIterator first, InputIterator last, const T& value);
+template<class ExecutionPolicy, class ForwardIterator,
+         class T = iterator_traits<ForwardIterator>::value_type>
+  typename iterator_traits<ForwardIterator>::difference_type
+    count(ExecutionPolicy&& exec,
+          ForwardIterator first, ForwardIterator last, const T& value);
+
+template<class InputIterator, class Predicate>
+  constexpr typename iterator_traits<InputIterator>::difference_type
+    count_if(InputIterator first, InputIterator last, Predicate pred);
+template<class ExecutionPolicy, class ForwardIterator, class Predicate>
+  typename iterator_traits<ForwardIterator>::difference_type
+    count_if(ExecutionPolicy&& exec,
+             ForwardIterator first, ForwardIterator last, Predicate pred);
+
+template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_for [iterator.concept.sentinel]")<I> S, class Proj = identity,
+         class T = projected_value_t<I, Proj>>
+  requires [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<I, Proj>, const T*>
+  constexpr iter_difference_t<I>
+    ranges::count(I first, S last, const T& value, Proj proj = {});
+template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity, class T = projected_value_t<iterator_t<R>, Proj>>
+  requires [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<iterator_t<R>, Proj>, const T*>
+  constexpr range_difference_t<R>
+    ranges::count(R&& r, const T& value, Proj proj = {});
+
+template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_access_iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_sentinel_for [iterator.concept.sizedsentinel]")<I> S,
+         class Proj = identity, class T = projected_value_t<I, Proj>>
+  requires [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<I, Proj>, const T*>
+  iter_difference_t<I>
+    ranges::count(Ep&& exec, I first, S last, const T& value, Proj proj = {});
+template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
+         class T = projected_value_t<iterator_t<R>, Proj>>
+  requires [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to,
+                                      projected<iterator_t<R>, Proj>, const T*>
+  range_difference_t<R> ranges::count(Ep&& exec, R&& r, const T& value, Proj proj = {});
+
+template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_for [iterator.concept.sentinel]")<I> S, class Proj = identity,
+         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
+  constexpr iter_difference_t<I>
+    ranges::count_if(I first, S last, Pred pred, Proj proj = {});
+template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
+         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
+  constexpr range_difference_t<R>
+    ranges::count_if(R&& r, Pred pred, Proj proj = {});
+
+template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_access_iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_sentinel_for [iterator.concept.sizedsentinel]")<I> S,
+         class Proj = identity, [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
+  iter_difference_t<I>
+    ranges::count_if(Ep&& exec, I first, S last, Pred pred, Proj proj = {});
+template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
+         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
+  range_difference_t<R>
+    ranges::count_if(Ep&& exec, R&& r, Pred pred, Proj proj = {});
+`
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L5436)
+
+Let E be:
+
+- [(1.1)](#1.1)
+
+*i == value for the overloads
+ with no parameter pred or proj;
+
+- [(1.2)](#1.2)
+
+pred(*i) != false for the overloads
+ with a parameter pred but no parameter proj;
+
+- [(1.3)](#1.3)
+
+invoke(proj, *i) == value for the overloads
+ with a parameter proj but no parameter pred;
+
+- [(1.4)](#1.4)
+
+bool(invoke(pred, invoke(proj, *i))) for the overloads
+ with both parameters proj and pred[.](#1.sentence-1)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L5453)
+
+*Effects*: Returns the number of iterators i in the range [first, last)
+for which E holds[.](#2.sentence-1)
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L5458)
+
+*Complexity*: Exactly last - first applications
+of the corresponding predicate and any projection[.](#3.sentence-1)