Parameter REACH : mem -> (block -> bool) -> block -> bool.Axiom REACHAX : (* Constructible via FiniteMaps.v, relying on finiteness of memories *)
  forall m B b, REACH m B b = true
  <-> exists L, reach m (fun bb => B bb = true) L b.

Lemma REACH_mono: forall B1 B2 (HB: forall b, B1 b = true -> B2 b = true) m b (R: REACH m B1 b = true), REACH m B2 b = true.