let V be RealLinearSpace; :: thesis: for V1, V2 being Subset of V st V1 is linearly-closed & V2 is linearly-closed holds
V1 /\ V2 is linearly-closed
let V1, V2 be Subset of V; :: thesis: ( V1 is linearly-closed & V2 is linearly-closed implies V1 /\ V2 is linearly-closed )
assume A1: ( V1 is linearly-closed & V2 is linearly-closed ) ; :: thesis: V1 /\ V2 is linearly-closed
thus for v, u being VECTOR of V st v in V1 /\ V2 & u in V1 /\ V2 holds
v + u in V1 /\ V2 :: according to RLSUB_1:def 1 :: thesis: for a being Real
for v being VECTOR of V st v in V1 /\ V2 holds
a * v in V1 /\ V2

proof

let v, u be VECTOR of V; :: thesis: ( v in V1 /\ V2 & u in V1 /\ V2 implies v + u in V1 /\ V2 )
assume ( v in V1 /\ V2 & u in V1 /\ V2 ) ; :: thesis: v + u in V1 /\ V2
then ( v in V1 & v in V2 & u in V1 & u in V2 ) by XBOOLE_0:def 4;
then ( v + u in V1 & v + u in V2 ) by A1, Def1;
hence v + u in V1 /\ V2 by XBOOLE_0:def 4; :: thesis: verum

end;

let a be Real; :: thesis: for v being VECTOR of V st v in V1 /\ V2 holds
a * v in V1 /\ V2
let v be VECTOR of V; :: thesis: ( v in V1 /\ V2 implies a * v in V1 /\ V2 )
assume v in V1 /\ V2 ; :: thesis: a * v in V1 /\ V2
then ( v in V1 & v in V2 ) by XBOOLE_0:def 4;
then ( a * v in V1 & a * v in V2 ) by A1, Def1;
hence a * v in V1 /\ V2 by XBOOLE_0:def 4; :: thesis: verum