meets all of the requirements of a container, of an
unordered associative container, and of an allocator-aware container
It provides the operations described in the
preceding requirements table for equivalent keys; that is, an unordered_multiset
supports the a_eq
operations in that table, not the a_uniq
For an unordered_multiset<Key>
the key type
and the value type are
types are both
constant iterator types.
It is unspecified whether they are the same type.