Goal:
  
  G : t
  HI : invariants G
  y_0 : V.t
  x_0 : V.t
  K : Z
  p1 : SPath G (V G') y_0 y_0
  HG : weight (to_pathOf G p1) <= 0
  Vx : VSet.In x_0 (V G)
  Vy : VSet.In y_0 (V G)
  Hxs : lsp G x_0 y_0 = None
  x : V.t
  p' : SPath G' (V G') y_0 x
  p2 : SPath G (V G') x_0 x
  ============================
   (forall x n : Z, n <= 0 -> n + x <= x)


DEBUG:Going to execute:
intros; Zify.zify_pre_hook; zify_elim_let; zify_op;
            Zify.zify_iter_specs