reserve x,y for object,X,Y,A,B,C,M for set;
reserve P,Q,R,R1,R2 for Relation;
reserve X,X1,X2 for Subset of A;
reserve Y for Subset of B;
reserve R,R1,R2 for Subset of [:A,B:];
reserve FR for Subset-Family of [:A,B:];
reserve R for Relation of A,B;
reserve S for Relation of B,C;

theorem :: (29.3)
  (id A)*R = R*(id B)
proof
  (id A)*R = R by FUNCT_2:17
    .= R*(id B) by FUNCT_2:17;
  hence thesis;
end;
