Definition lift (p : {poly F}) := map GRing.Const p.

Lemma rsumpT (p q : polyF) : rpoly p -> rpoly q -> rpoly (sumpT p q).
Fixpoint mulpT (p q : polyF) :=
if p isn't a :: p then [::]
else sumpT [seq (a * x)%T | x <- q] (0%T :: mulpT p q).