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 0: Backtrace:

Q is used in conclusion.
Level 0: Backtrace:

Q is used in conclusion.
Level 0: Backtrace:

Q is used in conclusion.
Level 0: Backtrace:

Q is used in conclusion.
Level 0: Backtrace:

Q is used in conclusion.
Level 1: Backtrace:

Q is used in conclusion.
Level 0: Backtrace:

Q is used in conclusion.