let V, W be non empty ModuleStr over INT.Ring ; :: thesis: for f being FrForm of V,W holds f + (NulFrForm (V,W)) = f
let f be FrForm of V,W; :: thesis: f + (NulFrForm (V,W)) = f
set g = NulFrForm (V,W);

now :: thesis: for v being Vector of V
for w being Vector of W holds (f + (NulFrForm (V,W))) . (v,w) = f . (v,w)

let v be Vector of V; :: thesis: for w being Vector of W holds (f + (NulFrForm (V,W))) . (v,w) = f . (v,w)
let w be Vector of W; :: thesis: (f + (NulFrForm (V,W))) . (v,w) = f . (v,w)
thus (f + (NulFrForm (V,W))) . (v,w) = (f . (v,w)) + ((NulFrForm (V,W)) . (v,w)) by Def2
.= (f . (v,w)) + (0. INT.Ring) by FUNCOP_1:70
.= f . (v,w) ; :: thesis: verum

end;

hence f + (NulFrForm (V,W)) = f ; :: thesis: verum