explicit multimap(const Compare& comp, const Allocator& = Allocator());
template<class InputIterator>
multimap(InputIterator first, InputIterator last,
const Compare& comp = Compare(),
const Allocator& = Allocator());
template<container-compatible-range<value_type> R>
multimap(from_range_t, R&& rg, const Compare& comp = Compare(), const Allocator& = Allocator());
template<class P> iterator insert(P&& x);
template<class P> iterator insert(const_iterator position, P&& x);
template<class Key, class T, class Compare, class Allocator, class Predicate>
typename multimap<Key, T, Compare, Allocator>::size_type
erase_if(multimap<Key, T, Compare, Allocator>& c, Predicate pred);