Díaz, Pablo A. “Absolutely Continuous Spectrum Preservation: A New Proof for Unitary Operators under Finite-Rank Multiplicative Perturbations”. CUBO, A Mathematical Journal 27, no. 3 (December 25, 2025): 701–712. Accessed December 27, 2025. https://cubo.ufro.cl/index.php/cubo/article/view/4198.