theorem Th16:
  W1 /\ W2 is Submodule of W1 & W1 /\ W2 is Submodule of W2
proof
  the carrier of W1 /\ W2 c= the carrier of W1 by Lm6;
  hence W1 /\ W2 is Submodule of W1 by RMOD_2:27;
  the carrier of W2 /\ W1 c= the carrier of W2 by Lm6;
  then the carrier of W1 /\ W2 c= the carrier of W2 by Th14;
  hence thesis by RMOD_2:27;
end;
