theorem :: ZMODLAT1:87
for V, W being non empty right_complementable vector-distributive scalar-distributive scalar-associative scalar-unital add-associative right_zeroed ModuleStr over INT.Ring
for v, u being Vector of V
for w, t being Vector of W
for a, b being Element of INT.Ring
for f being bilinear-FrForm of V,W holds f . ((v + (a * u)),(w + (b * t))) = ((f . (v,w)) + (b * (f . (v,t)))) + ((a * (f . (u,w))) + (a * (b * (f . (u,t)))))