proposition: Lemma rregM x y : rreg x -> rreg y -> rreg (x * y).
proof: Proof. by move=> reg_x reg_y; apply: (@lregM R^c). Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)