Goal:
  
  G : t
  HI : invariants
  HG : acyclic_no_loop
  x : VSet.elt
  Hx : VSet.In x (V G)
  e : lsp0 (V G) (s G) x = None
  p : PathOf (s G) x
  w : 0 <= weight p
  X : (Some (sweight (simplify2' p)) <= lsp0 (V G) (s G) x)%nbar
  ============================
   (exists n : Z, None = Some n /\ 0 <= n)


DEBUG:Going to execute:
rewrite e in   X