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


DEBUG:Going to execute:
assert X2
Level 1: evaluation returns
assert X2; [ exact (id0 id1) | clear id0 ]
where
id1 := H
of type
intropattern
id0 := n0
of type
intropattern
flags := 
of type
tauto_flags
X2 := False
of type
constr of type tacvalue