Goal:
  
  x1 : V.t
  n1 : Z
  y1 : V.t
  n2 : Z
  y2 : V.t
  x3 : V.t
  n3 : Z
  y3 : V.t
  H1 : V.lt x1 x3
  H2' : n2 < n3
  T1 : V.lt x1 x3 -> V.lt x3 x3 -> V.lt x1 x3
  T2 : V.lt y1 y2 -> V.lt y2 y3 -> V.lt y1 y3
  T3 : n1 = n2 -> n2 = n3 -> n1 = n3
  ============================
   (V.lt x1 x3 \/ x1 = x3 /\ n1 < n3 \/ x1 = x3 /\ n1 = n3 /\ V.lt y1 y3)


DEBUG:Going to execute:
assert X2
Level 1: evaluation returns
assert X2; [ exact (id0 id1) | clear id0 ]
where
id1 := H1
of type
intropattern
id0 := T1
of type
intropattern
flags := 
of type
tauto_flags
X2 := V.lt x3 x3 -> V.lt x1 x3
of type
constr of type tacvalue