let V be RealUnitarySpace; :: thesis: for W1, W2 being Subspace of V holds (0). W1 = (0). W2
let W1, W2 be Subspace of V; :: thesis: (0). W1 = (0). W2
(0). W1 = (0). V by Th30;
hence (0). W1 = (0). W2 by Th30; :: thesis: verum