Sorry for the lack of explanation. Combinations has a mathematinal definition more specialized and distinct from the usual dictionary version. Combinations are all the subsets of a set of a given size. So for the set (1,2,3,4) the combination of subsets with 2 elements is ((1,2),(1,3),(1,4),(2,3),(2,4),(3,4). The number of cominations of 4 elements chosen 2 at a time is called "4 choose 2)" or sometimes C(4,2) and in this case is equal to 6.

If one puts all the subsets generated from 4 choose 0, 4 choose 1, ..., 4 choose 4 into a set, that set of sets is called a power set of the original set.

I would implement combinations in p5 and then use the mythical p5 to p6 converter :) Just joking, but I haven't dived into p6 yet.