
theorem Th20:
  for C being with_identities non empty CategoryStr, a being Object of C holds
  a is terminal implies for h being Morphism of a,a holds id- a = h
proof
  let C be with_identities non empty CategoryStr, a be Object of C;
  assume a is terminal;
  then consider f being Morphism of a,a such that
A1: for g being Morphism of a,a holds f = g;
  let h be Morphism of a,a;
  id- a = f by A1;
  hence thesis by A1;
end;
