FRYDA, Jan. Orthogonality on the given hyperbolic planes. Annales Mathematicae Silesianae, [S. l.], v. 3, p. 132–137, 1990. Disponível em: https://journals.us.edu.pl/index.php/AMSIL/article/view/14312. Acesso em: 18 apr. 2025.