proposition: Lemma defPt_nullO A h x (v : A) (f : partition (x :-> v) h) : valid (untag f) -> x != null.
proof: Proof. by rewrite partitionE; apply: validPtUn_cond. Qed.
imports: Coq(ssreflect ssrbool ssrfun Eqdep) mathcomp(ssrnat eqtype seq path) pcm(options axioms finmap) pcm(pcm unionmap)