
theorem Th23:
  for P1,P2 being Element of absolute st tangent P1 = tangent P2 holds P1 = P2
  proof
    let P1,P2 be Element of absolute;
    assume
A1: tangent P1 = tangent P2;
    absolute /\ tangent P1 = {P1} & absolute /\ tangent P2 = {P2} by Th22;
    hence thesis by A1,ZFMISC_1:3;
  end;
