In combinatorial mathematics, a combination is an un-ordered collection of distinct elements, usually of a prescribed size and taken from a given set. (An ordered collection of distinct elements would sometimes be called a permutation, but that term is ambiguous; it can also mean "reordering of all terms", among other related notions.) Given such a set S, a combination of elements of S is just a subset of S, where, as always for (sub)sets the order of the elements isn't taken into account (two l… (More on Combination)