(** Heaps *)
Declare Instance Join_heap: Join heap.
Declare Instance Perm_heap: Perm_alg heap.
Declare Instance Sep_heap: Sep_alg heap.
Declare Instance Canc_heap: Canc_alg heap.
Parameter rawnext: forall (x: loc) (y : val) (s : heap), Prop.
Parameter emp_at : forall (l: loc) (h: heap), Prop.

Axiom mk_heap_rawnext : forall h x0 x y, val2loc (x0) = Some x ->
nil_or_loc y -> exists h', rawnext x y h' /\ comparable h h'.