Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  y_0 : V.t
  x_0 : V.t
  Vx : VSet.In x_0 (V G)
  Vy : VSet.In y_0 (V G)
  Hxs : lsp0 G (V G) x_0 y_0 = None
  K : Z
  x : VSet.elt
  Hx : VSet.In x (V G')
  p : SPath G' (V G) x x
  H : 0 <= sweight p
  p0 : SPath G (V G) x y_0 × SPath G (V G) x_0 x
  XX0 : sweight p = (let (q1, q2) := p0 in sweight q1 + K + sweight q2)
  XX := lsp0_spec_le G
          (simplify2' G (concat G (to_pathOf G p0.2) (to_pathOf G p0.1)))
     : (Some
          (sweight
             (simplify2' G (concat G (to_pathOf G p0.2) (to_pathOf G p0.1)))) <=
        lsp0 G (V G) x_0 y_0)%nbar
  ============================
   (Some (sweight p) = Some 0)


DEBUG:Going to execute:
rewrite -> Hxs in XX