proposition: Lemma lregX x n : lreg x -> lreg (x ^+ n).
proof: Proof. by move=> reg_x; elim: n => [|n]; [apply: lreg1 | rewrite exprS; apply: lregM]. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)