proposition: Lemma rem_rcons2 (T:eqType) (a: T) l: a \notin l -> rem a (rcons l a) = l.
proof: Proof. elim: l => [| b l H]; rewrite /= ?eqxx // inE /= eq_sym. by case: (b==a) => //=; move/H => ->. Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(seq path fintype div bigop binomial) mathcomp(prime finset ssralg ssrnum ssrint)