let V be RealUnitarySpace; :: thesis: for W1, W2 being Subspace of V holds the carrier of (W1 /\ W2) c= the carrier of W1
let W1, W2 be Subspace of V; :: thesis: the carrier of (W1 /\ W2) c= the carrier of W1
the carrier of (W1 /\ W2) = the carrier of W1 /\ the carrier of W2 by Def2;
hence the carrier of (W1 /\ W2) c= the carrier of W1 by XBOOLE_1:17; :: thesis: verum