Goal:
    A : Type  p : A → bool  a : A  l : list A  n : nat  x : A
  ============================
   (nth_error (a :: l) (S n) = Some x
    → let H := CoreTactics.block in
      forallb p (a :: l)
      → (∀ n : nat, nth_error l n = Some x → forallb p l → p x)
        → let H0 := CoreTactics.block in p x)


DEBUG:Going to execute:
intro || (let H := fresh in
                     intro
                     H)
DEBUG LTAC Evaluated term: (let H := CoreTactics.block in
                            forallb p (a :: l)
                            → (∀ n : nat,
                                 nth_error l n = Some x → forallb p l → p x)
                              → let H0 := CoreTactics.block in p x)
DEBUG LTAC Evaluated term: Prop