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'
  X0 : ∀ (i : nat) (x y : A), P i x y → Q i x y
  X1 : OnOne2i Q (S i) tl tl'
  ============================
   (OnOne2i Q (S i) tl tl')


DEBUG:Going to execute:
<Coq.Init.Tauto.flatten_contravariant_disj> flags X1 X2 id
Level 2: evaluation returns
<coq-core.plugins.tauto::flatten_contravariant_disj@0>
where
tauto_flags := 
of type
tauto_flags
id := P
of type
constr
X2 := A → A → Type
of type
constr
X1 := nat
of type
constr of type tacvalue

Level 2: Backtrace:

Tactic failure.
Level 2: Backtrace:

Tactic failure.
Level 1: Backtrace:

Tactic failure.