proposition: Lemma updiVm x m xs : x \in dom (updi x.+m xs) = [&& x != null, m == 0 & size xs > 0].
proof: Proof. case: m=>[|m] /=; last first. - by rewrite andbF; apply: negbTE; apply: updiVm'. case: xs=>[|v xs]; rewrite ptr0 ?andbF ?andbT //=. by rewrite domPtUn inE /= eq_refl -updiS updiD orbF andbT /=. Qed.
imports: mathcomp(ssreflect ssrfun ssrnat div ssrbool seq) LemmaOverloading(prelude finmap ordtype) mathcomp(path eqtype) Eqdep