reserve r for Real;

theorem Th21:
  for x,y being Element of 1 st x <> y holds 0 < Empty^2-to-zero.(x,y)
proof
  let x,y be Element of 1;
  x={} by CARD_1:49,TARSKI:def 1;
  hence thesis by CARD_1:49,TARSKI:def 1;
end;
