proposition: Lemma divKf x : x != 0 -> involutive (fun y => x / y).
proof: Proof. by move=> nz_x y; rewrite invf_div mulrC divfK. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)