Module: Mathlib.RingTheory.Spectrum.Prime.ChevalleyComplexity

Goal state before:
pp: case succ
R : Type u_2
inst✝ : CommRing R
n✝ n : ℕ
IH :
  ∀ {M : Submodule ℤ R},
    1 ∈ M →
      ∀ (k : ℕ) (d : Multiset (Fin n)) (S : ConstructibleSetData (MvPolynomial (Fin n) R)),
        (∀ C ∈ S, C.n ≤ k) →
          (∀ C ∈ S, ∀ (j : Fin C.n), C.g j ∈ coeffsIn (Fin n) M ⊓ Submodule.restrictScalars ℤ (degreesLE R (Fin n) d)) →
            ∃ T,
              comap MvPolynomial.C '' S.toSet = T.toSet ∧
                ∀ C ∈ T,
                  C.n ≤ numBound k (fun i ↦ 1 + Multiset.count i (Multiset.map Fin.val d)) n ∧
                    ∀ (i : Fin C.n), C.g i ∈ M ^ degBound k (fun i ↦ 1 + Multiset.count i (Multiset.map Fin.val d)) n
M : Submodule ℤ R
hM : 1 ∈ M
k : ℕ
d : Multiset (Fin (n + 1))
S : ConstructibleSetData (MvPolynomial (Fin (n + 1)) R)
hSn : ∀ C ∈ S, C.n ≤ k
hS :
  ∀ C ∈ S, ∀ (j : Fin C.n), C.g j ∈ coeffsIn (Fin (n + 1)) M ⊓ Submodule.restrictScalars ℤ (degreesLE R (Fin (n + 1)) d)
e : MvPolynomial (Fin (n + 1)) R ≃ₐ[R] (MvPolynomial (Fin n) R)[X] := MvPolynomial.finSuccEquiv R n
S' : ConstructibleSetData (MvPolynomial (Fin n) R)[X] := ConstructibleSetData.map e.toRingEquiv.toRingHom S
⊢ ∃ T,
    comap MvPolynomial.C '' S.toSet = T.toSet ∧
      ∀ C ∈ T,
        C.n ≤ numBound k (fun i ↦ 1 + Multiset.count i (Multiset.map Fin.val d)) (n + 1) ∧
          ∀ (i : Fin C.n), C.g i ∈ M ^ degBound k (fun i ↦ 1 + Multiset.count i (Multiset.map Fin.val d)) (n + 1)

Tactic:
have hS' : S'.degBound ≤ k * (1 + d.count 0) := by
    apply Finset.sup_le fun x hxS ↦ ?_
    simp only [ConstructibleSetData.map, RingEquiv.toRingHom_eq_coe,
      AlgEquiv.toRingEquiv_toRingHom, Finset.mem_image, BasicConstructibleSetData.map,
      RingHom.coe_coe, S'] at hxS
    obtain ⟨C, hxS, rfl⟩ := hxS
    trans ∑ i : Fin C.n, (1 + d.count 0)
    · gcongr with j hj
      simp only [e, comp_apply]
      by_cases hgj : C.g j = 0
      · rw [hgj, map_zero]
        simp
      rw [degree_finSuccEquiv hgj, WithBot.succ_natCast, add_comm]
      simp only [Nat.cast_id, add_le_add_iff_left, degreeOf_def]
      exact Multiset.count_le_of_le _ (hS _ hxS _).2
    · simp only [Finset.sum_const, Finset.card_univ, Fintype.card_fin, smul_eq_mul]
      gcongr
      exact hSn _ hxS

Goal state after:
case succ
R : Type u_2
inst✝ : CommRing R
n✝ n : ℕ
IH :
  ∀ {M : Submodule ℤ R},
    1 ∈ M →
      ∀ (k : ℕ) (d : Multiset (Fin n)) (S : ConstructibleSetData (MvPolynomial (Fin n) R)),
        (∀ C ∈ S, C.n ≤ k) →
          (∀ C ∈ S, ∀ (j : Fin C.n), C.g j ∈ coeffsIn (Fin n) M ⊓ Submodule.restrictScalars ℤ (degreesLE R (Fin n) d)) →
            ∃ T,
              comap MvPolynomial.C '' S.toSet = T.toSet ∧
                ∀ C ∈ T,
                  C.n ≤ numBound k (fun i ↦ 1 + Multiset.count i (Multiset.map Fin.val d)) n ∧
                    ∀ (i : Fin C.n), C.g i ∈ M ^ degBound k (fun i ↦ 1 + Multiset.count i (Multiset.map Fin.val d)) n
M : Submodule ℤ R
hM : 1 ∈ M
k : ℕ
d : Multiset (Fin (n + 1))
S : ConstructibleSetData (MvPolynomial (Fin (n + 1)) R)
hSn : ∀ C ∈ S, C.n ≤ k
hS :
  ∀ C ∈ S, ∀ (j : Fin C.n), C.g j ∈ coeffsIn (Fin (n + 1)) M ⊓ Submodule.restrictScalars ℤ (degreesLE R (Fin (n + 1)) d)
e : MvPolynomial (Fin (n + 1)) R ≃ₐ[R] (MvPolynomial (Fin n) R)[X] := MvPolynomial.finSuccEquiv R n
S' : ConstructibleSetData (MvPolynomial (Fin n) R)[X] := ConstructibleSetData.map e.toRingEquiv.toRingHom S
hS' : S'.degBound ≤ k * (1 + Multiset.count 0 d)
⊢ ∃ T,
    comap MvPolynomial.C '' S.toSet = T.toSet ∧
      ∀ C ∈ T,
        C.n ≤ numBound k (fun i ↦ 1 + Multiset.count i (Multiset.map Fin.val d)) (n + 1) ∧
          ∀ (i : Fin C.n), C.g i ∈ M ^ degBound k (fun i ↦ 1 + Multiset.count i (Multiset.map Fin.val d)) (n + 1)