proposition: Fact ffun_add0 : left_id ffun_zero ffun_add.
proof: Proof. by move=> f; apply/ffunP=> a; rewrite !ffunE add0r. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)