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 Th1:
  R c= [:dom R, rng R:]
proof
  let y,z;
  assume [y,z] in R;
  then y in dom R & z in rng R by XTUPLE_0:def 12,def 13;
  hence thesis by ZFMISC_1:87;
end;
