theorem EltsOfINTGroup2: :: TH83
  for x being object
  holds x in INT.Group 2 iff (x = 0 or x = 1)
proof
  let x be object;
  thus x in INT.Group 2 implies (x = 0 or x = 1)
  proof
    assume x in INT.Group 2;
    then x in Segm 2 by Th76;
    hence thesis by CARD_1:50,TARSKI:def 2;
  end;
  assume x = 0 or x = 1;
  then x in Segm 2 by CARD_1:50, TARSKI:def 2;
  hence x in INT.Group 2 by Th76;
end;
