# commutative

Two numbers, *x* and *z*, are said to be *commutative under
addition* if

*x* + *y* = *y* + *x*

and to be *commutative under multiplication* if

*x* × *y* = *xy* × *yx*

In general, two elements *a* and *b* of a set *S* are commutative under the binary operation (an operation that works
on two elements at a time) * if

*a* * *b* = *ab* * *ba*

Compare with associative and distributive.