-- Mathlib/LinearAlgebra/Eigenspace/Zero.lean
lemma hasEigenvalue_zero_tfae (φ : Module.End K M) :
    List.TFAE [
      Module.End.HasEigenvalue φ 0,
      IsRoot (minpoly K φ) 0,
      constantCoeff φ.charpoly = 0,
      LinearMap.det φ = 0,
      ⊥ < ker φ,
      ∃ (m : M), m ≠ 0 ∧ φ m = 0 ]

Proof state:
K : Type u_2
M : Type u_3
inst✝³ : Field K
inst✝² : AddCommGroup M
inst✝¹ : Module K M
inst✝ : Module.Finite K M
φ : End K M
tfae_1_iff_2 : φ.HasEigenvalue 0 ↔ (minpoly K φ).IsRoot 0
tfae_2_to_3 : (minpoly K φ).IsRoot 0 → constantCoeff (charpoly φ) = 0
tfae_3_to_4 : constantCoeff (charpoly φ) = 0 → LinearMap.det φ = 0
tfae_4_to_5 : LinearMap.det φ = 0 → ⊥ < ker φ
⊢ [φ.HasEigenvalue 0, (minpoly K φ).IsRoot 0, constantCoeff (charpoly φ) = 0, LinearMap.det φ = 0, ⊥ < ker φ,
      ∃ m, m ≠ 0 ∧ φ m = 0].TFAE

Tactic:
tfae_have 5 → 6 := by
  contrapose!
  simp only [not_bot_lt_iff, eq_bot_iff]
  intro h x
  simp only [mem_ker, Submodule.mem_bot]
  contrapose!
  apply h

Result:
K : Type u_2
M : Type u_3
inst✝³ : Field K
inst✝² : AddCommGroup M
inst✝¹ : Module K M
inst✝ : Module.Finite K M
φ : End K M
tfae_1_iff_2 : φ.HasEigenvalue 0 ↔ (minpoly K φ).IsRoot 0
tfae_2_to_3 : (minpoly K φ).IsRoot 0 → constantCoeff (charpoly φ) = 0
tfae_3_to_4 : constantCoeff (charpoly φ) = 0 → LinearMap.det φ = 0
tfae_4_to_5 : LinearMap.det φ = 0 → ⊥ < ker φ
tfae_5_to_6 : ⊥ < ker φ → ∃ m, m ≠ 0 ∧ φ m = 0
⊢ [φ.HasEigenvalue 0, (minpoly K φ).IsRoot 0, constantCoeff (charpoly φ) = 0, LinearMap.det φ = 0, ⊥ < ker φ,
      ∃ m, m ≠ 0 ∧ φ m = 0].TFAE

Proof state:
K : Type u_2
M : Type u_3
inst✝³ : Field K
inst✝² : AddCommGroup M
inst✝¹ : Module K M
inst✝ : Module.Finite K M
φ : End K M
tfae_1_iff_2 : φ.HasEigenvalue 0 ↔ (minpoly K φ).IsRoot 0
tfae_2_to_3 : (minpoly K φ).IsRoot 0 → constantCoeff (charpoly φ) = 0
tfae_3_to_4 : constantCoeff (charpoly φ) = 0 → LinearMap.det φ = 0
tfae_4_to_5 : LinearMap.det φ = 0 → ⊥ < ker φ
⊢ (∀ (m : M), m ≠ 0 → φ m ≠ 0) → ker φ ≤ ⊥

Tactic:
intro h x

Result:
K : Type u_2
M : Type u_3
inst✝³ : Field K
inst✝² : AddCommGroup M
inst✝¹ : Module K M
inst✝ : Module.Finite K M
φ : End K M
tfae_1_iff_2 : φ.HasEigenvalue 0 ↔ (minpoly K φ).IsRoot 0
tfae_2_to_3 : (minpoly K φ).IsRoot 0 → constantCoeff (charpoly φ) = 0
tfae_3_to_4 : constantCoeff (charpoly φ) = 0 → LinearMap.det φ = 0
tfae_4_to_5 : LinearMap.det φ = 0 → ⊥ < ker φ
h : ∀ (m : M), m ≠ 0 → φ m ≠ 0
x : M
⊢ x ∈ ker φ → x ∈ ⊥

Proof state:
K : Type u_2
M : Type u_3
inst✝³ : Field K
inst✝² : AddCommGroup M
inst✝¹ : Module K M
inst✝ : Module.Finite K M
φ : End K M
tfae_1_iff_2 : φ.HasEigenvalue 0 ↔ (minpoly K φ).IsRoot 0
tfae_2_to_3 : (minpoly K φ).IsRoot 0 → constantCoeff (charpoly φ) = 0
⊢ ((toMatrix (chooseBasis K M) (chooseBasis K M)) φ).charpoly.coeff 0 = 0 →
    (-1) ^ Fintype.card (ChooseBasisIndex K M) * ((toMatrix (chooseBasis K M) (chooseBasis K M)) φ).charpoly.coeff 0 = 0

Tactic:
intro h

Result:
K : Type u_2
M : Type u_3
inst✝³ : Field K
inst✝² : AddCommGroup M
inst✝¹ : Module K M
inst✝ : Module.Finite K M
φ : End K M
tfae_1_iff_2 : φ.HasEigenvalue 0 ↔ (minpoly K φ).IsRoot 0
tfae_2_to_3 : (minpoly K φ).IsRoot 0 → constantCoeff (charpoly φ) = 0
h : ((toMatrix (chooseBasis K M) (chooseBasis K M)) φ).charpoly.coeff 0 = 0
⊢ (-1) ^ Fintype.card (ChooseBasisIndex K M) * ((toMatrix (chooseBasis K M) (chooseBasis K M)) φ).charpoly.coeff 0 = 0

Proof state:
K : Type u_2
M : Type u_3
inst✝³ : Field K
inst✝² : AddCommGroup M
inst✝¹ : Module K M
inst✝ : Module.Finite K M
φ : End K M
tfae_1_iff_2 : φ.HasEigenvalue 0 ↔ (minpoly K φ).IsRoot 0
tfae_2_to_3 : (minpoly K φ).IsRoot 0 → constantCoeff (charpoly φ) = 0
tfae_3_to_4 : constantCoeff (charpoly φ) = 0 → LinearMap.det φ = 0
tfae_4_to_5 : LinearMap.det φ = 0 → ⊥ < ker φ
⊢ ⊥ < ker φ → ∃ m, m ≠ 0 ∧ φ m = 0

Tactic:
contrapose!

Result:
K : Type u_2
M : Type u_3
inst✝³ : Field K
inst✝² : AddCommGroup M
inst✝¹ : Module K M
inst✝ : Module.Finite K M
φ : End K M
tfae_1_iff_2 : φ.HasEigenvalue 0 ↔ (minpoly K φ).IsRoot 0
tfae_2_to_3 : (minpoly K φ).IsRoot 0 → constantCoeff (charpoly φ) = 0
tfae_3_to_4 : constantCoeff (charpoly φ) = 0 → LinearMap.det φ = 0
tfae_4_to_5 : LinearMap.det φ = 0 → ⊥ < ker φ
⊢ (∀ (m : M), m ≠ 0 → φ m ≠ 0) → ¬⊥ < ker φ