proposition: Lemma expansion_prop0P i: (inc i (domain f)) <-> i <c k.
proof: Proof. have [_ kn _ [_ -> _]] := Exp; apply: iff_sym ;exact: (NltP kn). Qed.
imports: mathcomp(ssreflect ssrfun ssrbool eqtype ssrnat) mathcomp(binomial div)