Goal:
  
  A : Type
  P : list A → list A → A → A → Type
  H1 : sigma (λ _ : list A, list A)
  H : All2_fold P (pr1 H1) (pr2 H1)
  Γ : list A
  ============================
   ({| pr1 := Γ; pr2 := Γ |} = H1
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in
      All_fold (λ (Γ : list A) (d : A), P Γ Γ d d) Γ)


DEBUG:Going to execute:
fun tac => lazymatch goal with
                      | H:_ |- _ => tac H
                      end