let V, W be non empty ModuleStr over INT.Ring ; :: thesis: for v, u being Vector of V
for w, t being Vector of W
for f being additiveFAF additiveSAF Form of V,W holds f . ((v + u),(w + t)) = ((f . (v,w)) + (f . (v,t))) + ((f . (u,w)) + (f . (u,t)))
let v, w be Vector of V; :: thesis: for w, t being Vector of W
for f being additiveFAF additiveSAF Form of V,W holds f . ((v + w),(w + t)) = ((f . (v,w)) + (f . (v,t))) + ((f . (w,w)) + (f . (w,t)))
let y, z be Vector of W; :: thesis: for f being additiveFAF additiveSAF Form of V,W holds f . ((v + w),(y + z)) = ((f . (v,y)) + (f . (v,z))) + ((f . (w,y)) + (f . (w,z)))
let f be additiveFAF additiveSAF Form of V,W; :: thesis: f . ((v + w),(y + z)) = ((f . (v,y)) + (f . (v,z))) + ((f . (w,y)) + (f . (w,z)))
set v1 = f . (v,y);
set v3 = f . (v,z);
set v4 = f . (w,y);
set v5 = f . (w,z);
thus f . ((v + w),(y + z)) = (f . (v,(y + z))) + (f . (w,(y + z))) by BLTh26
.= ((f . (v,y)) + (f . (v,z))) + (f . (w,(y + z))) by BLTh27
.= ((f . (v,y)) + (f . (v,z))) + ((f . (w,y)) + (f . (w,z))) by BLTh27 ; :: thesis: verum