If by subtraction is meant: remove elements of B that are in A or remove elements of A that are in B, then if A-B=B-A, A=B so the sets are identical, each containing the same elements as the other, but not necessarily in the same order. (If A and B contain no elements in common (their intersection is the empty set), A-B=A and B-A=B, so A-B is not equal to B-A. If the intersection of the sets is not empty, and A is not equal to B, then A-B is not equal to B-A.)