reserve e for set;
reserve C,C1,C2,C3 for AltCatStr;
reserve C for non empty AltCatStr,
  o for Object of C;

theorem Th23:
  for o9 being Object of ObCat o holds o9 = o
proof
  let o9 be Object of ObCat o;
  the carrier of ObCat o = {o} by Def12;
  hence thesis by TARSKI:def 1;
end;
