Goal:
  
  G : t
  HI : invariants
  HG : acyclic_no_loop
  x : V.t
  p : PathOf x (s G)
  H : VSet.In x (V G)
  lx : Z
  lsx : lsp (s G) x = Some lx
  w : 0 <= lx
  sp := simplify2' p : SPath (V G) x (s G)
  xs : Z
  lxs : lsp x (s G) = Some xs
  wxs : sweight sp <= xs
  ============================
   (xs + lx <= 0 -> sweight sp <= 0)


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