reserve UA for Universal_Algebra,
  f, g for Function of UA, UA;
reserve I for set,
  A, B, C for ManySortedSet of I;
reserve S for non void non empty ManySortedSign,
  U1, U2 for non-empty MSAlgebra over S;

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;
