reserve x,x1,x2,y,y9,y1,y2,z,z1,z2 for object,P,X,X1,X2,Y,Y1,Y2,V,Z for set;

theorem
  for f being Relation of X,Y holds f*(id Y) = f
proof
  let f be Relation of X,Y;
  rng f c= Y;
  hence thesis by RELAT_1:53;
end;
