Goal:
  
  G : t
  z : V.t
  x : V.t
  y : V.t
  z0 : V.t
  p : PathOf G y z0
  e : EdgeOf G z0 z
  i : V.t
  H : VSet.In z0 (nodes G (PathOf_add_end p e))
  source_vertex0 : VSet.In (s G) (V G)
  ============================
   (x = z0 \/ VSet.In z0 (nodes G p))


DEBUG:Going to execute:
<Coq.Init.Tauto.is_empty> flags X1; elim H
Level 6: evaluation returns
<coq-core.plugins.tauto::is_empty@0>
where
tauto_flags := 
of type
tauto_flags
X1 := t
of type
constr of type tacvalue

Level 6: Backtrace:

Tactic failure.
Level 6: Backtrace:

Tactic failure.
Level 5: Backtrace:

Tactic failure.
Level 5: Backtrace:

Tactic failure.