Goal:
  
  A : Type
  P : nat → A → A → Type
  Q : A → Type
  hd : A
  tl : list A
  i : nat
  hd' : A
  p : P i hd hd'
  X : Q hd
  X0 : All Q tl
  ============================
   (Q hd)


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.