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
  ============================
   (∀ (l : list A) (l0 : ∀ y : C, Q y → ∥ All (R y) l ∥) 
      (H := CoreTactics.block) (P : C → A → Prop) 
      (Q' : B → Type) (args : list A) (ha : ∀ y : C, Q y → ∥ All (R y) args ∥),
      {| pr1 := l; pr2 := l0 |} = {| pr1 := args; pr2 := ha |}
      → map_All f l l0 = map_All f args ha
        → let H0 := CoreTactics.block in
          (∀ y : C, Q y → All (P y) args)
          → (∀ (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 args ha))


DEBUG:Going to execute:
unshelve refine_ho elimt; intros; cbv beta;
            DepElim.simplify_dep_elim; CoreTactics.intros_until_block;
            DepElim.simplify_dep_elim;
            cbn beta iota
             delta [Prop.Logic.transport Logic.eq_elim Logic.eq_elim_r
                   eq_rect DepElim.pack_sigma_eq
                   DepElim.pack_sigma_eq_nondep] in *