proposition: Lemma Q2 : forall n, X (S n) = scal A (X n).
proof: Proof. intros n. rewrite /scal /= /Mmult. apply (coeff_mat_ext 0). case ; [ | case => //]. case ; [ | case => //] ; rewrite coeff_mat_bij /= ; (try lia) ; rewrite sum_Sn sum_O /plus /mult //=. case ; [ | case => //] ; rewrite coeff_mat_bij /= ; (try lia) ; rewrite sum_Sn sum_O /plus /mult //=. Qed.
imports: Coq(Reals Psatz ssreflect) Coquelicot(Hierarchy PSeries Rbar Lim_seq)