Description: The commutative law for binary operations, see definitions of laws A2.
and M2. in section 1.1 of Hall p. 1, or definition 8 in BourbakiAlg1
p. 7: the value of a binary operation applied to two operands equals the
value of a binary operation applied to the two operands in reversed
order. By this definition, the commutative law is expressed as binary
relation: a binary operation is related to a set by comLaw if the
commutative law holds for this binary operation regarding this set.
Note that the binary operation needs neither to be closed nor to be a
function. (Contributed by AV, 7-Jan-2020)