remove from unordered set c 2b 2b

1// By position:	iterator erase ( const_iterator position );
2// By key:		size_type erase ( const key_type& k );
3// By range:	iterator erase ( const_iterator first, const_iterator last );
4
5myset.erase ( myset.begin() );                    // erasing by iterator
6myset.erase ( "France" );                         // erasing by key
7myset.erase ( myset.find("Japan"), myset.end() ); // erasing by range