reserve A,X,X1,X2,Y,Y1,Y2 for set, a,b,c,d,x,y,z for object;
reserve P,P1,P2,Q,R,S for Relation;

theorem
  rng [:X,Y:] c= Y
proof
  let x be object;
  assume x in rng [:X,Y:];
  then ex y being object st [y,x] in [:X,Y:] by XTUPLE_0:def 13;
  hence thesis by ZFMISC_1:87;
end;
