Array, Hash, and Enumerable Combination / Array Notes in 'array.c' * ary.combination(n) { |c| block } -> ary * ary.combination(n) -> enumerator * * When invoked with a block, yields all combinations of length n * of elements from ary and then returns ary itself. * The implementation makes no guarantees about the order in which * the combinations are yielded. * * When invoked without a block, retur