insert

  #include <set>
  iterator insert( iterator pos, const TYPE& val );
  iterator insert( const TYPE& val );
  void insert( input_iterator start, input_iterator end );

The function insert() either:

• inserts val after the element at pos (where pos is really just a suggestion as to where val should go, since multisets and multimaps are ordered), and returns an iterator to that element.
• inserts val into the multiset, returning an iterator to the element inserted.
• inserts a range of elements from start to end.