Goal:
  
  G : t
  HI : invariants G
  HG : acyclic_no_loop G
  n : Z
  x : V.t
  y : V.t
  n0 : x = y -> False
  ============================
   (False -> false = true <-> x = y)


DEBUG:Going to execute:
intro; clear id
Level 2: evaluation returns
<coq-core.plugins.ltac::cut@0>
where
$1 := False
of type
constr of type tacvalue