-- Lean 4 proof step from Mathlib.RingTheory.Spectrum.Prime.ChevalleyComplexity (goal)
Goal:
R_1 : Type u_2
inst : CommRing R_1
n : ℕ
R : Type u_2
inst_1 : CommRing R
c : InductionObj R n
i j : Fin n
hi : (c.val i).Monic
hle : (c.val i).degree ≤ (c.val j).degree
hne : i ≠ j
H :
  ∀ {R₀ : Type u_1} [inst : CommRing R₀] [inst_4 : Algebra R₀ R],
    Statement R₀ R n
      { val := Function.update (β := fun (a : Fin n) ↦ R[X]) c.val j (c.val j %ₘ c.val i) : InductionObj R n }
R₀ : Type u_1
inst_2 : CommRing R₀
inst_3 : Algebra R₀ R
f : R[X]
h : Nontrivial R
S : ConstructibleSetData R
hS :
  comap Polynomial.C ''
      (zeroLocus
          (Set.range
            { val := Function.update (β := fun (a : Fin n) ↦ R[X]) c.val j (c.val j %ₘ c.val i) :
                InductionObj R n }.val) \
        zeroLocus {f}) =
    S.toSet
hS' :
  ∀ C ∈ S,
    C.n ≤
        { val := Function.update (β := fun (a : Fin n) ↦ R[X]) c.val j (c.val j %ₘ c.val i) :
            InductionObj R n }.degBound ∧
      ∀ (i_1 : Fin C.n),
        C.g i_1 ∈
          HPow.hPow (α := Submodule R₀ R)
            (coeffSubmodule R₀
              { val := Function.update (β := fun (a : Fin n) ↦ R[X]) c.val j (c.val j %ₘ c.val i) : InductionObj R n })
            { val := Function.update (β := fun (a : Fin n) ↦ R[X]) c.val j (c.val j %ₘ c.val i) :
                InductionObj R n }.powBound
C : BasicConstructibleSetData R
hC : C ∈ S
c' : InductionObj R n := { val := Function.update (β := fun (a : Fin n) ↦ R[X]) c.val j (c.val j %ₘ c.val i) }
deg_bound₁ : c'.degBound ≤ c.degBound
k : Fin C.n
⊢ HPow.hPow (α := Submodule R₀ R) (coeffSubmodule R₀ c') (c'.degBound ^ c'.degBound) ≤
    HPow.hPow (α := Submodule R₀ R) (coeffSubmodule R₀ c) (c.degBound ^ c.degBound)
have hP₃ : coeffSubmodule R₀ c' ≤ HPow.hPow (α := Submodule R₀ R) (coeffSubmodule R₀ c) (c.val j).degree.succ
Tactic: suffices hij : c'.coeffSubmodule R₀ ≤ c.coeffSubmodule R₀ ^ (c.val j).degree.succ by
        by_cases hi' : c.val i = 1
        · gcongr
          · exact c.one_le_coeffSubmodule
          · refine Submodule.span_le.mpr (Set.union_subset ?_ ?_)
            · exact Set.subset_union_left.trans Submodule.subset_span
            · refine Set.iUnion_subset fun k ↦ ?_
              simp only [update_apply, hi', modByMonic_one, c']
              split_ifs
              · rintro _ ⟨_, rfl⟩
                exact zero_mem _
              · exact (Set.subset_iUnion (fun i ↦ coeff(c.val i)) k).trans
                  (Set.subset_union_right.trans Submodule.subset_span)
          rw [Nat.one_le_iff_ne_zero, ← Nat.pos_iff_ne_zero, InductionObj.degBound]
          refine Fintype.sum_pos (Pi.lt_def.mpr ⟨by positivity, i, by simp [hi']⟩)
        refine (pow_le_pow_left' hij _).trans ?_
        rw [← pow_mul]
        apply pow_le_pow_right' c.one_le_coeffSubmodule
        have deg_bound₂ : c'.degBound < c.degBound := by
          dsimp [InductionObj.degBound, c']
          apply Finset.sum_lt_sum ?_ ⟨j, Finset.mem_univ _, ?_⟩
          · intro k _
            rw [update_apply]
            split_ifs with hkj
            · subst hkj; gcongr; exact (degree_modByMonic_le _ hi).trans hle
            · rfl
          · gcongr; simpa using (degree_modByMonic_lt _ hi).trans_le hle
        calc (c.val j).degree.succ * c'.degBound ^ c'.degBound
          _ ≤ c.degBound * c.degBound ^ c'.degBound := by
            gcongr
            delta InductionObj.degBound
            exact Finset.single_le_sum (f := fun i ↦ (c.val i).degree.succ)
              (by intros; positivity) (Finset.mem_univ _)
          _ = c.degBound ^ (c'.degBound + 1) := by rw [pow_succ']
          _ ≤ c.degBound ^ c.degBound := by gcongr <;> lia