theorem Th26:
  for f1, f2 be Element of MSAAut U1 holds f1 ** f2 in MSAAut U1
proof
  let f1, f2 be Element of MSAAut U1;
  f1 is_isomorphism U1, U1 & f2 is_isomorphism U1, U1 by Def5;
  then f1 ** f2 is_isomorphism U1, U1 by MSUALG_3:15;
  hence thesis by Def5;
end;
