Goal:
  
  G : t
  HG : acyclic_no_loop
  s : VSet.t
  x : V.t
  y1 : V.t
  y2 : V.t
  n : Z
  He : EdgeSet.In (y1, n, y2) (E G)
  Hy : VSet.In y1 s
  ============================
   (forall z : Z,
    lsp0 s x y1 = Some z -> (Some z + Some n <= lsp0 s x y2)%nbar)


DEBUG:Going to execute:
idtac
DEBUG LTAC Evaluated term: (lsp0 s x y1)