New EdgeSubGraphWrapper class specializing SubGraphWrapper in the way that only the edge-set can be filtered.
     3 #include <lemon/maps.h>
 
    10   ConstMap<int, char> a('#');
 
    12   cout << "sizeof ConstMap<int,char> = " << sizeof a << endl;
 
    13   cout << "a[5] = " << a[5] << endl;
 
    15   StdMap<int, char> b('$');
 
    16   cout << "sizeof ConstMap<int,char> = " << sizeof b << endl;
 
    17   cout << "sizeof std::map<int,char> = "
 
    18        << sizeof(std::map<int,char>) << endl;
 
    19   cout << "b[5] = " << b[5] << endl;
 
    22   cout << "b[5] = " << b[5] << endl;