template<typename ForwardIterator>
inline SPROUT_CONSTEXPR bool
is_decreasing(ForwardIterator first, ForwardIterator last);
#include <sprout/algorithm/is_decreasing.hpp>
#include <sprout/array.hpp>
#include <sprout/container.hpp>
using namespace sprout;
SPROUT_STATIC_CONSTEXPR auto input = array<int, 10>{{5, 5, 4, 4, 3, 3, 2, 2, 1, 1}};
SPROUT_STATIC_CONSTEXPR auto result = sprout::is_decreasing(begin(input), end(input));
static_assert(result, "input is decreasing.");