reserve R for non empty Poset,
  S1 for OrderSortedSign;

theorem Th8:
  for U1 being OSAlgebra of S1 holds U1,U1 are_os_isomorphic
proof
  let U1 be OSAlgebra of S1;
  take id (the Sorts of U1);
  the Sorts of U1 is OrderSortedSet of S1 by OSALG_1:17;
  hence thesis by MSUALG_3:16;
end;
