Goal:
  
  A : Type
  B : Type
  C : Type
  Q : C → Type
  P : C → A → Prop
  Q' : B → Type
  R : C → A → Prop
  f : ∀ x : A, (∀ y : C, Q y → R y x) → B
  args : list A
  ha : ∀ y : C, Q y → ∥ All (R y) args ∥
  packcall : let H := map_All f in
             sigma (λ l : list A, ∀ y : C, Q y → ∥ All (R y) l ∥)
  ============================
   (packcall = {| pr1 := args; pr2 := ha |}
    → map_All f (pr1 packcall) (pr2 packcall) =
      map_All f (pr1 {| pr1 := args; pr2 := ha |})
        (pr2 {| pr1 := args; pr2 := ha |})
      → let H := 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:
with_last_secvar_aux tac
Level 2: evaluation returns
with_last_secvar_aux tac + orelse
where
tac := fun eos => move packcall before eos
       where
       tac := fun _ => idtac
              where
              c := map_All f args ha
              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 f
       of type
       constr
       elimc := fun_elim
       of type
       constr
       c := map_All f args ha
       of type
       constr
       Heq := Heqcall
       of type
       intropattern
       H := eqargs
       of type
       intropattern
of type
tacvalue
orelse := move packcall at top
          where
          tac := fun _ => idtac
                 where
                 c := map_All f args ha
                 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 f
          of type
          constr
          elimc := fun_elim
          of type
          constr
          c := map_All f args ha
          of type
          constr
          Heq := Heqcall
          of type
          intropattern
          H := eqargs
          of type
          intropattern
of type
tacvalue of type tacvalue