theorem
  for V being torsion-free Z_Module,
  W1, W2 being finite-rank free Subspace of V
  st rank(W1 + W2) = rank(W2) holds
  rank(W1 /\ W2) = rank(W1)
  proof
    let V be torsion-free Z_Module ,
    W1, W2 be finite-rank free Subspace of V;
    assume rank(W1 + W2) = rank(W2); then
    rank(W2) + rank(W1 /\ W2) = rank(W1) + rank(W2) by LmISRank51X;
    hence thesis;
end;
