proposition: Fact sub_fun_is_additive : additive (f \- g).
proof: Proof. by move=> x y /=; rewrite !raddfB addrAC -!addrA -!opprD addrAC addrA. Qed.
imports: HB(structures) mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat div seq) mathcomp(choice fintype finfun bigop prime binomial)