Goal:
  
  A : Type
  P : list A → list A → A → A → Type
  d : A
  Γ : list A
  X : All_fold (λ (Γ : list A) (d : A), P Γ Γ d d) Γ
  p : P Γ Γ d d
  IHX : All2_fold P Γ Γ
  ============================
   (P Γ Γ d d)


DEBUG:Going to execute:
fun id0 id1 X2 => assert X2; [ exact (id0 id1) | clear id0 ]