Goal:
  
  A : Type
  P : list A → list A → A → A → Type
  Q : list A → list A → A → A → Type
  d : A
  d' : A
  Γ : list A
  Γ' : list A
  X : All2_fold (λ (Γ Δ : list A) (x y : A), P Γ Δ x y × Q Γ Δ x y) Γ Γ'
  p : P Γ Γ' d d' × Q Γ Γ' d d'
  IHX : All2_fold P Γ Γ' × All2_fold Q Γ Γ'
  ============================
   (All2_fold P Γ Γ')


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