Goal:
  
  A : Type
  B : Type
  f : A → B
  l : list A
  g : ∀ x : A, In x l → B
  Heqg : g = λ (x : A) (_ : In x l), f x
  packcall : let H := @map_In in
             sigma
               (λ A : Type,
                  sigma
                    (λ B : Type, sigma (λ l : list A, ∀ x : A, In x l → B)))
  ============================
   (∀ eqargs : packcall =
               {|
                 pr1 := A;
                 pr2 := {| pr1 := B; pr2 := {| pr1 := l; pr2 := g |} |}
               |},
      eq_rect packcall
        (λ projs : sigma
                     (λ A : Type,
                        sigma
                          (λ B : Type,
                             sigma (λ l : list A, ∀ x : A, In x l → B))),
           list (pr1 (pr2 projs)))
        (map_In (pr1 (pr2 (pr2 packcall))) (pr2 (pr2 (pr2 packcall))))
        {|
          pr1 := A; pr2 := {| pr1 := B; pr2 := {| pr1 := l; pr2 := g |} |}
        |} eqargs =
      map_In
        (pr1
           (pr2
              (pr2
                 {|
                   pr1 := A;
                   pr2 := {| pr1 := B; pr2 := {| pr1 := l; pr2 := g |} |}
                 |})))
        (pr2
           (pr2
              (pr2
                 {|
                   pr1 := A;
                   pr2 := {| pr1 := B; pr2 := {| pr1 := l; pr2 := g |} |}
                 |}))) → let H := CoreTactics.block in map_In l g = map f l)


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_In l g
              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_In
       of type
       constr
       elimc := fun_elim
       of type
       constr
       c := map_In l g
       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_In l g
                 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_In
          of type
          constr
          elimc := fun_elim
          of type
          constr
          c := map_In l g
          of type
          constr
          Heq := Heqcall
          of type
          intropattern
          H := eqargs
          of type
          intropattern
of type
tacvalue of type tacvalue