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Coding Standards
boost::container::flat_multiset
// In header: <boost/container/flat_set.hpp> template<typename InputIterator> flat_multiset(ordered_range_t, InputIterator, InputIterator);
Deduction guide: allows a flat_multiset to be constructed from an already ordered iterator range [first, last), deducing the key type from InputIterator and using the default comparator and allocator.