(** ** Preservation of a property over solutions *)
Definition Pstate (st: state) : Prop :=
forall pc, P st.(aval)!!pc.

(* Specifications: *)
Lemma propagate_successors_P:
forall bb l,
P l ->
forall succs st,
Pstate st ->
Pstate (propagate_successors bb succs l st).
Theorem fixpoint_invariant:
forall res pc, fixpoint = Some res -> P res!!pc.