Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  n : Z
  x : V.t
  e : EdgeSet.elt
  Hle : leq_vertices G n x e..t
  Vy : ~ VSet.In e..t (V G)
  H : EdgeSet.In e (E G)
  n0 : e..s <> e..t
  ============================
   (EdgeSet.In e (E G))


DEBUG:Going to execute:
solve
[ trivial
with eq_true
| reflexivity
| symmetry; trivial
| contradiction
| congruence ]