proposition: Lemma der_cont n : GFunctor.continuous (@derived_at n).
proof: Proof. by move=> aT rT G f; rewrite morphim_der. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat fintype) mathcomp(bigop finset binomial fingroup morphism) mathcomp(automorphism quotient gfunctor)