begin
Lm1:
for V being RealUnitarySpace
for x being set holds
( x in (0). V iff x = 0. V )
Lm2:
for V being RealUnitarySpace
for W1, W2, W3 being Subspace of V st W1 is Subspace of W3 holds
W1 /\ W2 is Subspace of W3
Lm3:
for V being RealUnitarySpace
for W1, W2, W3 being Subspace of V st W1 is Subspace of W2 & W1 is Subspace of W3 holds
W1 is Subspace of W2 /\ W3
Lm4:
for V being RealUnitarySpace
for W1, W2, W3 being Subspace of V st W1 is Subspace of W2 holds
W1 is Subspace of W2 + W3
Lm5:
for V being RealUnitarySpace
for W1, W2, W3 being Subspace of V st W1 is Subspace of W3 & W2 is Subspace of W3 holds
W1 + W2 is Subspace of W3
begin
begin
Lm6:
for X, x being set st not x in X holds
X \ {x} = X
begin
begin