theorem
  id X /\ EqR = id X
proof
  now
    let x,y be object;
    assume [x,y] in id X;
    then x in X & x = y by RELAT_1:def 10;
    hence [x,y] in EqR by Th5;
  end;
  then id X c= EqR;
  hence thesis by XBOOLE_1:28;
end;
