Other assumptions required are that the negation of a relation is a relation, and that the logical product of a class of relations (i.e. the assertion of all of them simultaneously) is a relation. Also the relative product of two relations must be a relation. The relative product of two relations R, S is the relation which holds between x and z whenever there is a term y towhich x has the relation R and which has to z the relation S. Thus the relation of a maternal grandfather to his grandson is the relative produt of father and mother