Hello. You can find a new version of my class to the sandbox file vault (flos_junction.zip). It implements some of the ideas from this discussion. But it's very inefficient, because it makes a lot of copies. I don't like the implementation, but it works and has the semantic I visualized. Probaly I will need some help to make it more efficient. I see junctions as a expressive way to write comparisons and aritmethic operations on lists and as a alternative to loops. Furthermore I must note that Perls junctions are not limited to sets. Junctions are more general. They can be applied to any list and are a logical linkage between the elements of the list, which determines the result of a comparison. That's exactly what my class implements. There are now four classes: conjunction<T>, disjunction<T>, abjunction<T> and injunction<T>. Whereas T is a Container-Type. And the Functions all_of, any_of, one_of, none_of create instances of this classes from a container. See the examples. There is a base class junction, becaus elsewise I don't know how to support all the operators and circumvent writing duplicate code (There are already a lot of macros ;-). Is there a better way? Sincerly Florian