Chmieliński, Jacek. “On the Superstability of the Generalized Orthogonality Equation in Euclidean Spaces”. Annales Mathematicae Silesianae 8 (September 30, 1994): 127–140. Accessed April 11, 2025. https://journals.us.edu.pl/index.php/AMSIL/article/view/14224.