Goal:
  
  A : Type
  P : nat → A → Type
  Q : A → Type
  n : nat
  hd : A
  tl : list A
  p : P n hd
  X : Alli P (S n) tl
  IHX : All Q tl → Alli (λ (k : nat) (x : A), P k x × Q x) (S n) tl
  X0 : All Q (hd :: tl)
  x : A
  l : list A
  X1 : Q hd
  X2 : All Q tl
  H0 : x = hd
  H1 : l = tl
  ============================
   (Alli (λ (k : nat) (x : A), P k x × Q x) (S n) 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.