-step must bring us back to our starting-point. With other relations, this is by no means the case; for example, if
is the relation of child to parent, the relative product of
and its converse is the relation "self or brother or sister," and if
is the relation of grandchild to grandparent, the relative product of
and its converse is "self or brother or sister or first cousin." It will be observed that the relative product of two relations is not in general commutative, i.e. the relative product of