proposition: Lemma fmorphV : {morph f: x / x^-1}.
proof: Proof. move=> x; have [-> | nz_x] := eqVneq x 0; first by rewrite !(invr0, rmorph0). by rewrite rmorphV ?unitfE. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)