Definition oracle (ent: entailment) : bool :=
 match VeriStar.check_entailment ent with
 | VeriStar.Valid => true
 | VeriStar.C_example _ => false
 | VeriStar.Aborted _ _ => false
 end.Definition incon (a: assertion) : bool :=
   oracle (Entailment a
               (Assertion (Nequ Nil Nil :: nil)
                              match a with (Assertion _ sigma) => sigma end)).

(* Specifications: *)
Lemma eq_expr (e1 e2: expr) : {e1=e2}+{e1<>e2}.