Goal:
  
  A : Type
  P : A → Prop
  Q : A → Prop
  a : A
  l' : list A
  X : All P []
  X0 : All Q (a :: l')
  H : 0 = S #|l'|
  ============================
   (All2 (λ x y : A, P x ∧ Q y) [] (a :: l'))


DEBUG:Going to execute:
apply : eq_sym ; trivial
Level 0: Backtrace:

Proof is not complete.
Level 0: Backtrace:

Proof is not complete.