consider v being Vector of , w being Vector of such that
A1: f . v,w <> 0. K by Th41;
reconsider B = w + (RKer f) as Vector of by VECTSP10:24;
reconsider A = v + (LKer f) as Vector of by VECTSP10:24;
(QForm f) . A,B = f . v,w by Def23;
hence not QForm f is constant by A1, Th41; :: thesis: verum