Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  n : Z
  x : V.t
  y : V.t
  Vy : ~ VSet.In y (V G)
  Hle : leq_vertices G n x y
  nneg : n <= 0
  n0 : x <> y
  z : Z
  H : lsp G x (s G) = Some z
  mem : VSet.mem x (V G) = false
  H0 : z = 0
  ============================
   (n <= z)


DEBUG:Going to execute:
lazymatch Zify.zify_convert_to_euclidean_division_equations_flag
           with
           | true =>
               Zify.zify_internal_to_euclidean_division_equations
           | false => idtac
           end