Local Notation "a <===> b" := (heq a b) (at level 60).Definition emp := emp.Definition inj := fun p => (prop p && emp).Definition star := sepcon.Definition ex := @exp mpred Nveric.Ltac sep_solve :=
  unfold star, himp, heq, emp, inj, ex in *; intuition; cancel; auto.Module Sep := SepExpr.Make VericSepLogic.

Lemma isnil: forall {T: Type} (s: list T), {s=nil}+{s<>nil}.