Goal:
  
  x1 : V.t
  n1 : Z
  y1 : V.t
  x2 : V.t
  n2 : Z
  y2 : V.t
  x3 : V.t
  n3 : Z
  y3 : V.t
  H1 : V.lt x1 x2
  H2 : V.lt x2 x3
  T2 : V.lt y1 y2 -> V.lt y2 y3 -> V.lt y1 y3
  T3 : n1 = n2 -> n2 = n3 -> n1 = n3
  H : V.lt x2 x3 -> V.lt x1 x3
  ============================
   (V.lt x1 x3 \/ x1 = x3 /\ n1 < n3 \/ x1 = x3 /\ n1 = n3 /\ V.lt y1 y3)


DEBUG:Going to execute:
PTRDEBUGTACF x2 x1 x0
Level 2: evaluation returns
<coq-core.plugins.tauto::find_cut@0>
where
k := fun id0 id1 X2 => assert X2; [ exact (id0 id1) | clear id0 ]
     where
     flags := 
     of type
     tauto_flags
of type
tacvalue of type tacvalue