Qed.

Lemma Rbilinear_non_zero_2:forall a b c d x y x' y', y<>0 -> y'<>0 ->
(a*(x/y)*(x'/y')+b*(x/y)+c*(x'/y')+d<>0)%R -> (a*x*x'+b*x*y'+c*y*x'+d*y*y'<>0)%R.