Goal:
  
  A : Type
  B : Type
  C : Type
  Q : C → Type
  P : C → A → Prop
  fn : ∀ x : A, (∀ y : C, Q y → P y x) → B
  l : list A
  H : ∀ y : C, Q y → ∥ All (P y) l ∥
  n : nat
  x : A
  H0 : nth_error l n = Some x
  ============================
   (∃ D : ∀ y : C, Q y → P y x, nth_error (map_All fn l H) n = Some (fn x D))


DEBUG:Going to execute:
CoreTactics.block_goal; uncurry_call elimfn c packcall packcall_fn;
            remember_let packcall_fn; unfold_packcall packcall;
            refine (DepElim.eq_simplification_sigma1 _ _ _ _ _) ||
              refine (DepElim.eq_simplification_sigma1_nondep_dep _ _ _ _ _)
               || refine (DepElim.eq_simplification_sigma1_dep _ _ _ _ _)
Level 4: evaluation returns
CoreTactics.block_goal; uncurry_call elimfn c packcall packcall_fn;
 remember_let packcall_fn; unfold_packcall packcall;
 refine (DepElim.eq_simplification_sigma1 _ _ _ _ _) ||
   refine (DepElim.eq_simplification_sigma1_nondep_dep _ _ _ _ _) || refine
    (DepElim.eq_simplification_sigma1_dep _ _ _ _ _);
 (let H := fresh "eqargs" in
  let Heq := fresh "Heqcall" in
  intros H Heq; try (rewrite <- Heq; clear Heq); CoreTactics.revert_until H;
   revert H; subst packcall_fn; clearbody packcall;
   make_packcall packcall elimfn;
   with_last_secvar ltac:(fun eos => move packcall before eos)
    ltac:(move packcall at top); CoreTactics.revert_until packcall;
   CoreTactics.block_goal; cbv zeta in packcall; revert packcall; curry;
   (let elimt := make_refine elimn elimc in
    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 *; DepElim.simplify_IH_hyps; CoreTactics.unblock_goal;
     DepElim.simplify_IH_hyps; tac c))
where
tac := fun _ => idtac
       where
       c := map_All fn l H
       of type
       constr
of type
tacvalue
packcall_fn := packcall_fn
of type
intropattern
packcall := packcall
of type
intropattern
elimn := 3
of type
constr
elimfn := map_All fn
of type
constr
elimc := fun_elim
of type
constr
c := map_All fn l H
of type
constr of type tacvalue

Level 3: evaluation returns
CoreTactics.block_goal; uncurry_call elimfn c packcall packcall_fn;
 remember_let packcall_fn; unfold_packcall packcall;
 refine (DepElim.eq_simplification_sigma1 _ _ _ _ _) ||
   refine (DepElim.eq_simplification_sigma1_nondep_dep _ _ _ _ _) || refine
    (DepElim.eq_simplification_sigma1_dep _ _ _ _ _);
 (let H := fresh "eqargs" in
  let Heq := fresh "Heqcall" in
  intros H Heq; try (rewrite <- Heq; clear Heq); CoreTactics.revert_until H;
   revert H; subst packcall_fn; clearbody packcall;
   make_packcall packcall elimfn;
   with_last_secvar ltac:(fun eos => move packcall before eos)
    ltac:(move packcall at top); CoreTactics.revert_until packcall;
   CoreTactics.block_goal; cbv zeta in packcall; revert packcall; curry;
   (let elimt := make_refine elimn elimc in
    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 *; DepElim.simplify_IH_hyps; CoreTactics.unblock_goal;
     DepElim.simplify_IH_hyps; tac c))
where
tac := fun _ => idtac
       where
       c := map_All fn l H
       of type
       constr
of type
tacvalue
packcall_fn := packcall_fn
of type
intropattern
packcall := packcall
of type
intropattern
elimn := 3
of type
constr
elimfn := map_All fn
of type
constr
elimc := fun_elim
of type
constr
c := map_All fn l H
of type
constr of type tacvalue

Level 2: evaluation returns
CoreTactics.block_goal; uncurry_call elimfn c packcall packcall_fn;
 remember_let packcall_fn; unfold_packcall packcall;
 refine (DepElim.eq_simplification_sigma1 _ _ _ _ _) ||
   refine (DepElim.eq_simplification_sigma1_nondep_dep _ _ _ _ _) || refine
    (DepElim.eq_simplification_sigma1_dep _ _ _ _ _);
 (let H := fresh "eqargs" in
  let Heq := fresh "Heqcall" in
  intros H Heq; try (rewrite <- Heq; clear Heq); CoreTactics.revert_until H;
   revert H; subst packcall_fn; clearbody packcall;
   make_packcall packcall elimfn;
   with_last_secvar ltac:(fun eos => move packcall before eos)
    ltac:(move packcall at top); CoreTactics.revert_until packcall;
   CoreTactics.block_goal; cbv zeta in packcall; revert packcall; curry;
   (let elimt := make_refine elimn elimc in
    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 *; DepElim.simplify_IH_hyps; CoreTactics.unblock_goal;
     DepElim.simplify_IH_hyps; tac c))
where
tac := fun _ => idtac
       where
       c := map_All fn l H
       of type
       constr
of type
tacvalue
packcall_fn := packcall_fn
of type
intropattern
packcall := packcall
of type
intropattern
elimn := 3
of type
constr
elimfn := map_All fn
of type
constr
elimc := fun_elim
of type
constr
c := map_All fn l H
of type
constr of type tacvalue