
theorem Th28:
  for C,D being non empty category st C is trivial & D is trivial holds C ~= D
  proof
    let C,D be non empty category;
    assume C is trivial & D is trivial;
    then C ~= OrdC 1 & D ~= OrdC 1 by Th27;
    hence C ~= D by Th10;
  end;
