Kucia, Anna, and Andrzej Nowak. “On Carathéodory Type Selectors in a Hilbert Space”. Annales Mathematicae Silesianae 2 (September 30, 1986): 47–52. Accessed May 8, 2025. https://trrest.vot.pl/ojsus/index.php/AMSIL/article/view/14320.