Definition heap : Type := fpm nat nat.
Instance Join_heap: Join heap := Join_fpm (Join_discrete _).
Instance Perm_heap: Perm_alg heap := Perm_fpm _ (Perm_discrete nat).
Definition mapsto  (x y: nat) : pred heap :=
fun h => forall z, if eq_dec z x then lookup_fpm h z = Some y else lookup_fpm h z = None.
Inductive lis' : nat -> pred heap :=
| lis_nil : forall p w, (!!(p=0) && emp)%pred w -> lis' p w
| lis_cons: forall p w, (!!(p<>0) && EX r:nat, mapsto p r * lis' r)%pred w -> lis' p w.

Lemma lis'_fold_unfold:
forall p, lis' p =  (!!(p=0) && emp || !!(p<>0) && EX r:nat, mapsto p r * lis' r)%pred.