let V be RealLinearSpace; :: thesis: for W1, W2 being Subspace of V
for C1 being Coset of W1
for C2 being Coset of W2 st C1 meets C2 holds
C1 /\ C2 is Coset of W1 /\ W2

let W1, W2 be Subspace of V; :: thesis: for C1 being Coset of W1
for C2 being Coset of W2 st C1 meets C2 holds
C1 /\ C2 is Coset of W1 /\ W2

let C1 be Coset of W1; :: thesis: for C2 being Coset of W2 st C1 meets C2 holds
C1 /\ C2 is Coset of W1 /\ W2

let C2 be Coset of W2; :: thesis: ( C1 meets C2 implies C1 /\ C2 is Coset of W1 /\ W2 )
set v = the Element of C1 /\ C2;
set C = C1 /\ C2;
assume A1: C1 /\ C2 <> {} ; :: according to XBOOLE_0:def 7 :: thesis: C1 /\ C2 is Coset of W1 /\ W2
then reconsider v = the Element of C1 /\ C2 as Element of V by TARSKI:def 3;
v in C2 by ;
then A2: C2 = v + W2 by RLSUB_1:78;
v in C1 by ;
then A3: C1 = v + W1 by RLSUB_1:78;
C1 /\ C2 is Coset of W1 /\ W2
proof
take v ; :: according to RLSUB_1:def 6 :: thesis: C1 /\ C2 = v + (W1 /\ W2)
thus C1 /\ C2 c= v + (W1 /\ W2) :: according to XBOOLE_0:def 10 :: thesis: v + (W1 /\ W2) c= C1 /\ C2
proof
let x be object ; :: according to TARSKI:def 3 :: thesis: ( not x in C1 /\ C2 or x in v + (W1 /\ W2) )
assume A4: x in C1 /\ C2 ; :: thesis: x in v + (W1 /\ W2)
then x in C1 by XBOOLE_0:def 4;
then consider u1 being VECTOR of V such that
A5: u1 in W1 and
A6: x = v + u1 by ;
x in C2 by ;
then consider u2 being VECTOR of V such that
A7: u2 in W2 and
A8: x = v + u2 by ;
u1 = u2 by ;
then u1 in W1 /\ W2 by A5, A7, Th3;
hence x in v + (W1 /\ W2) by A6; :: thesis: verum
end;
let x be object ; :: according to TARSKI:def 3 :: thesis: ( not x in v + (W1 /\ W2) or x in C1 /\ C2 )
assume x in v + (W1 /\ W2) ; :: thesis: x in C1 /\ C2
then consider u being VECTOR of V such that
A9: u in W1 /\ W2 and
A10: x = v + u by RLSUB_1:63;
u in W2 by ;
then A11: x in { (v + u2) where u2 is VECTOR of V : u2 in W2 } by A10;
u in W1 by ;
then x in { (v + u1) where u1 is VECTOR of V : u1 in W1 } by A10;
hence x in C1 /\ C2 by ; :: thesis: verum
end;
hence C1 /\ C2 is Coset of W1 /\ W2 ; :: thesis: verum