-- Mathlib/Analysis/CStarAlgebra/Spectrum.lean
theorem unitary.spectrum_subset_circle (u : unitary E) :
    spectrum 𝕜 (u : E) ⊆ Metric.sphere 0 1

Proof state:
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
⊢ σ 𝕜 ↑u ⊆ Metric.sphere 0 1

Tactic:
nontriviality E

Result:
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
⊢ σ 𝕜 ↑u ⊆ Metric.sphere 0 1

Proof state:
case refine_2
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
k : 𝕜
hk : k ∈ σ 𝕜 ↑u
⊢ 1 ≤ ‖k‖

Tactic:
rw [← unitary.val_toUnits_apply u] at hk

Result:
case refine_2
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
k : 𝕜
hk : k ∈ σ 𝕜 ↑(toUnits u)
⊢ 1 ≤ ‖k‖

Proof state:
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
⊢ σ 𝕜 ↑u ⊆ Metric.sphere 0 1

Tactic:
refine fun k hk => mem_sphere_zero_iff_norm.mpr (le_antisymm ?_ ?_)

Result:
case refine_1
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
k : 𝕜
hk : k ∈ σ 𝕜 ↑u
⊢ ‖k‖ ≤ 1

case refine_2
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
k : 𝕜
hk : k ∈ σ 𝕜 ↑u
⊢ 1 ≤ ‖k‖

Proof state:
case refine_2
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
k : 𝕜
hk : k⁻¹ ∈ σ 𝕜 ↑(toUnits u)⁻¹
hnk : k ≠ 0
⊢ 1 ≤ ‖k‖

Tactic:
have : ‖k‖⁻¹ ≤ ‖(↑(unitary.toUnits u)⁻¹ : E)‖ := by
  simpa only [norm_inv] using norm_le_norm_of_mem hk

Result:
case refine_2
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
k : 𝕜
hk : k⁻¹ ∈ σ 𝕜 ↑(toUnits u)⁻¹
hnk : k ≠ 0
this : ‖k‖⁻¹ ≤ ‖↑(toUnits u)⁻¹‖
⊢ 1 ≤ ‖k‖

Proof state:
case refine_2
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
k : 𝕜
hk : k ∈ σ 𝕜 ↑(toUnits u)
⊢ 1 ≤ ‖k‖

Tactic:
have hnk := ne_zero_of_mem_of_unit hk

Result:
case refine_2
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
k : 𝕜
hk : k ∈ σ 𝕜 ↑(toUnits u)
hnk : k ≠ 0
⊢ 1 ≤ ‖k‖

Proof state:
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
k : 𝕜
hk : k⁻¹ ∈ σ 𝕜 ↑(toUnits u)⁻¹
hnk : k ≠ 0
⊢ ‖k‖⁻¹ ≤ ‖↑(toUnits u)⁻¹‖

Tactic:
simpa only [norm_inv] using norm_le_norm_of_mem hk

Result:
no goals

Proof state:
case refine_1
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
k : 𝕜
hk : k ∈ σ 𝕜 ↑u
⊢ ‖k‖ ≤ 1

Tactic:
simpa only [CStarRing.norm_coe_unitary u] using norm_le_norm_of_mem hk

Result:
no goals

Proof state:
case refine_2
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
k : 𝕜
hk : k⁻¹ ∈ σ 𝕜 ↑(toUnits u)⁻¹
hnk : k ≠ 0
this : ‖k‖⁻¹ ≤ ‖↑(toUnits u)⁻¹‖
⊢ 1 ≤ ‖k‖

Tactic:
simpa using inv_le_of_inv_le₀ (norm_pos_iff.mpr hnk) this

Result:
no goals

Proof state:
case refine_2
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
k : 𝕜
hk : k ∈ σ 𝕜 ↑(toUnits u)
hnk : k ≠ 0
⊢ 1 ≤ ‖k‖

Tactic:
rw [← inv_inv (unitary.toUnits u), ← spectrum.map_inv, Set.mem_inv] at hk

Result:
case refine_2
𝕜 : Type u_1
inst✝⁵ : NormedField 𝕜
E : Type u_2
inst✝⁴ : NormedRing E
inst✝³ : StarRing E
inst✝² : CStarRing E
inst✝¹ : NormedAlgebra 𝕜 E
inst✝ : CompleteSpace E
u : ↥(unitary E)
a✝ : Nontrivial E
k : 𝕜
hk : k⁻¹ ∈ σ 𝕜 ↑(toUnits u)⁻¹
hnk : k ≠ 0
⊢ 1 ≤ ‖k‖