I've often wished that STL sets supported set arithmetic operations. Addition, multiplication and subtraction operators could be overloaded with set union, intersection and difference respectively. For example: set<char> s1; // s1 <- {} s1 += 'a'; // s1 <- {a} set<char> s2 = s1 + 'b'; // s2 <- {a,b} set<char> s3 = s2 - s1; // s3 <- {b} set<char> s4 = s1 * s2; // s4 <- {a} Achieving the above results with the existing STL library is by comparison cumbersome, error-prone and unclear. Although this proposal does not follow the STL design philosophy, it meets a real developer need. It can be implemented using global operator overloads, which should avoid conflicts with other uses of STL sets. Comments and suggestions welcome. Best Regards Dominic Herity Red Plain Technology (www.redplain.com) T:+353-87-2208233 F: +1-603-909 6570 E: dominic.herity@redplain.com