Goal:
  
  A : Type
  P : A → Type
  Q : A → Type
  x : A
  l : list A
  p : P x
  Hl : All P l
  q : Q x
  Hl' : All Q l
  X : All (λ x : A, P x × Q x) l
  ============================
   (All (λ x : A, P x × Q x) (x :: l))


DEBUG:Going to execute:
match goal with
           | |- ?X1 → ?X2 => intro
           | |- ¬ _ => unfold not at 1; intro
           end