proposition: Lemma natr_aut nu x : (nu x \is a nat_num) = (x \is a nat_num).
proof: Proof. by apply/idP/idP=> /[dup] ? /(aut_natr nu) => [/fmorph_inj <-| ->]. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat seq choice) mathcomp(fintype bigop order ssralg poly ssrnum ssrint)