Goal:
  
  A : Type
  P : list A → list A → A → A → Type
  P' : list A → list A → A → A → Type
  d : A
  d' : A
  Γ : list A
  Γ' : list A
  cr : All2_fold P Γ Γ'
  p : P Γ Γ' d d'
  Hcr : ∀ (Γ Δ : list A) (d d' : A),
          All2_fold P Γ Δ → All2_fold P' Γ Δ → P Γ Δ d d' → P' Γ Δ d d'
  IHcr : All2_fold P' Γ Γ'
  ============================
   (All2_fold P' Γ Γ')


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