Goal:
  
  A : Type
  P : A → A → Type
  Q : A → A → Type
  x : A
  y : A
  l : list A
  l' : list A
  X : All2 (Trel_conj P Q) l l'
  a : P x y
  b : Q x y
  a0 : All2 P l l'
  b0 : All2 Q l l'
  ============================
   (All2 P l l')


DEBUG:Going to execute:
F x2 x1 x0
Level 0: Backtrace:

Q is used in hypothesis X.
Level 0: Backtrace:

Q is used in hypothesis X.
Level 0: Backtrace:

Q is used in hypothesis X.
Level 0: Backtrace:

Q is used in hypothesis X.
Level 0: Backtrace:

Q is used in hypothesis X.
Level 1: Backtrace:

Q is used in hypothesis X.
Level 0: Backtrace:

Q is used in hypothesis X.