Goal:
  
  A : Type
  B : Type
  C : Type
  Q : C → Type
  R : C → A → Prop
  f : ∀ x : A, (∀ y : C, Q y → R y x) → B
  x : A
  xs : list A
  h : ∀ y : C, Q y → ∥ All (R y) (x :: xs) ∥
  X : ∀ (P : C → A → Prop) (Q' : B → Type),
        (∀ y : C, Q y → All (P y) xs)
        → (∀ (x : A) (y : C) (rx : ∀ y0 : C, Q y0 → R y0 x),
             P y x → Q' (f x rx))
          → ∀ y : C,
              Q y → All Q' (map_All f xs (map_All_obligation_2 x xs h))
  P : C → A → Prop
  Q' : B → Type
  ha : ∀ y : C, Q y → All (P y) (x :: xs)
  hf : ∀ (x : A) (y : C) (rx : ∀ y0 : C, Q y0 → R y0 x), P y x → Q' (f x rx)
  y : C
  hy : Q y
  p : P y x
  X0 : All (P y) xs
  y0 : C
  p0 : P y0 x
  X1 : All (P y0) xs
  ============================
   (let H := CoreTactics.block in
    let H0 := CoreTactics.block in All (P y0) xs)


DEBUG:Going to execute:
match goal with
           | |- let _ := CoreTactics.block in ?T =>
                 match T with
                 | context [ CoreTactics.block ] =>
                     change T; CoreTactics.intros_until_block
                 end
           | _ => CoreTactics.unblock_goal
           end