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(** ** Stacks as evaluation contexts                                    *)
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(** Here is a quick lemma that uses the properties defined above. It shows that the stack behaves like an *evaluation context*, lifting a small-step reduction to a larger term. *)

(* Specifications: *)
Lemma apply_stack_cong : forall s h e e',
step e e' ->
step (apply_stack h s e) (apply_stack h s e').