Goal:
  
  A : Type
  P : nat → A → A → Type
  Q : nat → A → A → Type
  i : nat
  hd : A
  tl : list A
  tl' : list A
  X : OnOne2i P (S i) tl tl'
  IHX : (∀ (i : nat) (x y : A), P i x y → Q i x y) → OnOne2i Q (S i) tl tl'
  X0 : ∀ (i : nat) (x y : A), P i x y → Q i x y
  ============================
   (OnOne2i Q (S i) tl tl')


DEBUG:Going to execute:
F 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