Goal:
  
  A : Type
  f : A → bool
  l : list A
  g : ∀ x : A, In x l → bool
  Heqg : g = λ (x : A) (_ : In x l), f x
  packcall : let H := forallb_InP in
             sigma (λ l : list A, ∀ x : A, In x l → bool)
  ============================
   (packcall = {| pr1 := l; pr2 := g |}
    → forallb_InP (pr1 packcall) (pr2 packcall) =
      forallb_InP (pr1 {| pr1 := l; pr2 := g |})
        (pr2 {| pr1 := l; pr2 := g |})
      → let H := CoreTactics.block in forallb_InP l g = forallb 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 := forallb_InP 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 := forallb_InP
       of type
       constr
       elimc := fun_elim
       of type
       constr
       c := forallb_InP 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 := forallb_InP 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 := forallb_InP
          of type
          constr
          elimc := fun_elim
          of type
          constr
          c := forallb_InP l g
          of type
          constr
          Heq := Heqcall
          of type
          intropattern
          H := eqargs
          of type
          intropattern
of type
tacvalue of type tacvalue