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9 changes: 7 additions & 2 deletions Mathlib/Algebra/Star/Unitary.lean
Original file line number Diff line number Diff line change
Expand Up @@ -406,16 +406,21 @@ variable {R A : Type*} [CommSemiring R] [Ring A] [Algebra R A] [StarMul A]

/-- Unitary conjugation preserves the spectrum, star on left. -/
@[simp]
lemma spectrum.unitary_conjugate {a : A} {u : unitary A} :
lemma _root_.spectrum.unitary_star_right_conjugate {a : A} {u : unitary A} :
spectrum R (u * a * (star u : A)) = spectrum R a :=
spectrum.units_conjugate (u := unitary.toUnits u)

/-- Unitary conjugation preserves the spectrum, star on right. -/
@[simp]
lemma spectrum.unitary_conjugate' {a : A} {u : unitary A} :
lemma _root_.spectrum.unitary_star_left_conjugate {a : A} {u : unitary A} :
spectrum R ((star u : A) * a * u) = spectrum R a := by
simpa using spectrum.unitary_conjugate (u := star u)

@[deprecated (since := "2025-10-20")] alias spectrum.unitary_conjugate :=
spectrum.unitary_star_right_conjugate
@[deprecated (since := "2025-10-20")] alias spectrum.unitary_conjugate' :=
spectrum.unitary_star_left_conjugate'

end UnitaryConjugate

end unitary
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Original file line number Diff line number Diff line change
Expand Up @@ -110,7 +110,7 @@ instance instContinuousFunctionalCalculus :
apply Set.eq_of_subset_of_subset
· rw [← ContinuousMap.spectrum_eq_range f]
apply AlgHom.spectrum_apply_subset
· rw [cfcAux_apply, unitary.spectrum.unitary_conjugate]
· rw [cfcAux_apply, spectrum.unitary_star_right_conjugate]
rintro - ⟨x, rfl⟩
apply spectrum.of_algebraMap_mem 𝕜
simp only [Function.comp_apply, Set.mem_range, spectrum_diagonal]
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