Module Sep := SepExpr.Make VericSepLogic.

(*Definition if_then_else_isnil (b : forall (s: list val), {s=nil}+{s<>nil}) (m1 m2 : mpred) := if b then m1 else m2. *)
Lemma isnil: forall {T: Type} (s: list T), {s=nil}+{s<>nil}.