reserve GF for add-associative right_zeroed right_complementable Abelian
  associative well-unital distributive non empty doubleLoopStr;
reserve M for Abelian add-associative right_zeroed right_complementable
  vector-distributive scalar-distributive scalar-associative scalar-unital
   non empty ModuleStr over GF;
reserve W,W1,W2,W3 for Subspace of M;
reserve u,u1,u2,v,v1,v2 for Element of M;
reserve X,Y for set, x,y,y1,y2 for object;

theorem Th14:
  W1 /\ (W2 /\ W3) = (W1 /\ W2) /\ W3
proof
  set V1 = the carrier of W1;
  set V2 = the carrier of W2;
  set V3 = the carrier of W3;
  the carrier of W1 /\ (W2 /\ W3) = V1 /\ (the carrier of W2 /\ W3) by Def2
    .= V1 /\ (V2 /\ V3) by Def2
    .= (V1 /\ V2) /\ V3 by XBOOLE_1:16
    .= (the carrier of W1 /\ W2) /\ V3 by Def2;
  hence thesis by Def2;
end;
