theorem Th17:
  for S be non void non empty ManySortedSign, X be non-empty
  ManySortedSet of the carrier of S holds FreeMSA(X) is free
proof
  let S be non void non empty ManySortedSign, X be non-empty ManySortedSet of
  the carrier of S;
  take FreeGen(X);
  thus thesis by Th16;
end;
