(** The interface of the solver is similar to that of Kildall's forward solver, with a slightly different statement of the invariant preservation property [fixpoint_invariant]. *)
Module Type BBLOCK_SOLVER.
Declare Module L: ORDERED_TYPE_WITH_TOP.
Parameter fixpoint:
forall {A: Type} (code: PTree.t A) (successors: A -> list positive)
(transf: positive -> L.t -> L.t)
(entrypoint: positive),
option (PMap.t L.t).

Axiom fixpoint_solution:
forall A (code: PTree.t A) successors transf entrypoint res n instr s,
fixpoint code successors transf entrypoint = Some res ->
code!n = Some instr -> In s (successors instr) ->
L.ge res!!s (transf n res!!n).