Goal:
  
  G : t
  invG : invariants G
  acG : acyclic_no_loop G
  x : V.t
  y : V.t
  hx : VSet.In x (V G)
  hy : VSet.In y (V G)
  nxy : Z
  hxy : (lsp G x y <= Some nxy)%nbar
  nx : Z
  eqlspx : lsp G (s G) x = Some nx
  nxpos : 0 <= nx
  eqnx : Z.of_nat (to_label (lsp G (s G) x)) = nx
  ny : Z
  eqlspy : lsp G (s G) y = Some ny
  nypos : 0 <= ny
  eqny : Z.of_nat (to_label (lsp G (s G) y)) = ny
  ============================
   ((Some nx + lsp G x y <= Some ny)%nbar ->
    (lsp G x y <= Some nxy)%nbar ->
    ny - (nx + Z.of_nat (Z.to_nat (ny - nx - nxy))) <= nxy)


DEBUG:Going to execute:
case  E: (lsp _ _ _)  => [?|] //=
DEBUG LTAC Evaluated term: l'_on_x
DEBUG LTAC Evaluated term: l'_on_x
DEBUG LTAC Evaluated term: l'_on_y
DEBUG LTAC Evaluated term: l'_on_y
DEBUG LTAC Evaluated term: Nat2Z.inj_add
DEBUG LTAC Evaluated term: Nat2Z.inj_add
DEBUG LTAC Evaluated term: dxy
DEBUG LTAC Evaluated term: dxy
DEBUG LTAC Evaluated term: stdl
DEBUG LTAC Evaluated term: stdl
DEBUG LTAC Evaluated term: eqnx
DEBUG LTAC Evaluated term: eqnx
DEBUG LTAC Evaluated term: eqny
DEBUG LTAC Evaluated term: eqny
DEBUG LTAC Evaluated term: eqlspx
DEBUG LTAC Evaluated term: eqlspx
DEBUG LTAC Evaluated term: eqlspy
DEBUG LTAC Evaluated term: eqlspy