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
  ============================
   (x :: xs = []
    → let H := CoreTactics.block in
      let H0 := CoreTactics.block in All (P y0) xs)


DEBUG:Going to execute:
match goal with
           | |- context [ rew <- [_] eq_refl in _ ] =>
                 progress simpl eq_rect_r
           | |- context [ rew [_] eq_refl in _ ] => progress simpl eq_rect
           | |- context [ Prop.Logic.transport _ eq_refl _ ] =>
                 progress simpl Prop.Logic.transport
           | |- context [ Logic.eq_elim _ _ _ _ _ eq_refl ] =>
                 progress simpl eq_rect
           | |- context [ Logic.eq_elim_r _ _ _ _ eq_refl ] =>
                 progress simpl Logic.eq_elim_r
           | |- context [ noConfusion_inv _ ] =>
                 progress simpl noConfusion_inv
           | |- DepElim.opaque_ind_pack_eq_inv ?G eq_refl =>
                 apply (DepElim.simplify_ind_pack_inv B x p G)
           | |- let _ := CoreTactics.block in _ => fail 1
           | |- _ => simplify * || simplify ?; cbv beta
           | |- _ → ?B =>
                 let ty := type of B in
                 intro || (let H := fresh in
                           intro
                           H)
           | |- ∀ x, _ => let H := fresh x in
                          intro
                          H
           | |- _ => intro
           end