-- Mathlib/Analysis/BoxIntegral/Box/SubboxInduction.lean
theorem subbox_induction_on' {p : Box ι → Prop} (I : Box ι)
    (H_ind : ∀ J ≤ I, (∀ s, p (splitCenterBox J s)) → p J)
    (H_nhds : ∀ z ∈ Box.Icc I, ∃ U ∈ 𝓝[Box.Icc I] z, ∀ J ≤ I, ∀ (m : ℕ), z ∈ Box.Icc J →
      Box.Icc J ⊆ U → (∀ i, J.upper i - J.lower i = (I.upper i - I.lower i) / 2 ^ m) → p J) :
    p I

Proof state:
ι : Type u_1
p : Box ι → Prop
I : Box ι
H_nhds :
  ∀ z ∈ Box.Icc I,
    ∃ U ∈ 𝓝[Box.Icc I] z,
      ∀ J ≤ I,
        ∀ (m : ℕ),
          z ∈ Box.Icc J → Box.Icc J ⊆ U → (∀ (i : ι), J.upper i - J.lower i = (I.upper i - I.lower i) / 2 ^ m) → p J
hpI : ¬p I
s : Box ι → Set ι
hs : ∀ J ≤ I, ¬p J → ¬p (J.splitCenterBox (s J))
J : ℕ → Box ι := fun m => (fun J => J.splitCenterBox (s J))^[m] I
⊢ False

Tactic:
have J_succ : ∀ m, J (m + 1) = splitCenterBox (J m) (s <| J m) :=
  fun m ↦ iterate_succ_apply' _ _ _

Result:
ι : Type u_1
p : Box ι → Prop
I : Box ι
H_nhds :
  ∀ z ∈ Box.Icc I,
    ∃ U ∈ 𝓝[Box.Icc I] z,
      ∀ J ≤ I,
        ∀ (m : ℕ),
          z ∈ Box.Icc J → Box.Icc J ⊆ U → (∀ (i : ι), J.upper i - J.lower i = (I.upper i - I.lower i) / 2 ^ m) → p J
hpI : ¬p I
s : Box ι → Set ι
hs : ∀ J ≤ I, ¬p J → ¬p (J.splitCenterBox (s J))
J : ℕ → Box ι := fun m => (fun J => J.splitCenterBox (s J))^[m] I
J_succ : ∀ (m : ℕ), J (m + 1) = (J m).splitCenterBox (s (J m))
⊢ False

Proof state:
ι : Type u_1
p : Box ι → Prop
I : Box ι
H_nhds :
  ∀ z ∈ Box.Icc I,
    ∃ U ∈ 𝓝[Box.Icc I] z,
      ∀ J ≤ I,
        ∀ (m : ℕ),
          z ∈ Box.Icc J → Box.Icc J ⊆ U → (∀ (i : ι), J.upper i - J.lower i = (I.upper i - I.lower i) / 2 ^ m) → p J
hpI : ¬p I
s : Box ι → Set ι
hs : ∀ J ≤ I, ¬p J → ¬p (J.splitCenterBox (s J))
J : ℕ → Box ι := fun m => (fun J => J.splitCenterBox (s J))^[m] I
J_succ : ∀ (m : ℕ), J (m + 1) = (J m).splitCenterBox (s (J m))
hJmono : Antitone J
hJle : ∀ (m : ℕ), J m ≤ I
m✝ m : ℕ
⊢ ¬p (J m) → ¬p (J m.succ)

Tactic:
simpa only [J_succ] using hs (J m) (hJle m)

Result:
no goals

Proof state:
ι : Type u_1
p : Box ι → Prop
I : Box ι
H_nhds :
  ∀ z ∈ Box.Icc I,
    ∃ U ∈ 𝓝[Box.Icc I] z,
      ∀ J ≤ I,
        ∀ (m : ℕ),
          z ∈ Box.Icc J → Box.Icc J ⊆ U → (∀ (i : ι), J.upper i - J.lower i = (I.upper i - I.lower i) / 2 ^ m) → p J
hpI : ¬p I
H_ind : ∀ J ≤ I, ¬p J → ¬∀ (s : Set ι), p (J.splitCenterBox s)
⊢ False

Tactic:
simp only [exists_imp, not_forall] at H_ind

Result:
ι : Type u_1
p : Box ι → Prop
I : Box ι
H_nhds :
  ∀ z ∈ Box.Icc I,
    ∃ U ∈ 𝓝[Box.Icc I] z,
      ∀ J ≤ I,
        ∀ (m : ℕ),
          z ∈ Box.Icc J → Box.Icc J ⊆ U → (∀ (i : ι), J.upper i - J.lower i = (I.upper i - I.lower i) / 2 ^ m) → p J
hpI : ¬p I
H_ind : ∀ J ≤ I, ¬p J → ∃ x, ¬p (J.splitCenterBox x)
⊢ False

Proof state:
ι : Type u_1
p : Box ι → Prop
I : Box ι
H_nhds :
  ∀ z ∈ Box.Icc I,
    ∃ U ∈ 𝓝[Box.Icc I] z,
      ∀ J ≤ I,
        ∀ (m : ℕ),
          z ∈ Box.Icc J → Box.Icc J ⊆ U → (∀ (i : ι), J.upper i - J.lower i = (I.upper i - I.lower i) / 2 ^ m) → p J
hpI : ¬p I
s : Box ι → Set ι
hs : ∀ J ≤ I, ¬p J → ¬p (J.splitCenterBox (s J))
⊢ False

Tactic:
set J : ℕ → Box ι := fun m ↦ (fun J ↦ splitCenterBox J (s J))^[m] I

Result:
ι : Type u_1
p : Box ι → Prop
I : Box ι
H_nhds :
  ∀ z ∈ Box.Icc I,
    ∃ U ∈ 𝓝[Box.Icc I] z,
      ∀ J ≤ I,
        ∀ (m : ℕ),
          z ∈ Box.Icc J → Box.Icc J ⊆ U → (∀ (i : ι), J.upper i - J.lower i = (I.upper i - I.lower i) / 2 ^ m) → p J
hpI : ¬p I
s : Box ι → Set ι
hs : ∀ J ≤ I, ¬p J → ¬p (J.splitCenterBox (s J))
J : ℕ → Box ι := fun m => (fun J => J.splitCenterBox (s J))^[m] I
⊢ False