proposition: Lemma upd_nullP : x != null -> null \notin supp f -> null \notin supp (ins x d f).
proof: Proof. by move=>H1 H2; rewrite supp_ins negb_or /= eq_sym H1. Qed.
imports: mathcomp(ssreflect ssrfun ssrnat div ssrbool seq) LemmaOverloading(prelude finmap ordtype) mathcomp(path eqtype) Eqdep