Goal:
  
  G : t
  HI : invariants G
  x : VSet.elt
  s0 : SPath G (V G) x x
  HG : weight (to_pathOf G s0) <= 0
  y_0 : V.t
  x_0 : V.t
  Vx : VSet.In x_0 (V G)
  Vy : VSet.In y_0 (V G)
  Hxs : lsp G x_0 y_0 = None
  K : Z
  Hx : VSet.In x (V G')
  p : SPath G' (V G) x x
  H : 0 <= sweight p
  XX : sweight p = weight (to_pathOf G s0)
  ============================
   (sweight p = 0)


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