FRYDA, Jan. Orthogonality on the given hyperbolic planes. Annales Mathematicae Silesianae, [S. l.], v. 3, p. 132–137, 1990. Disponível em: https://trrest.vot.pl/ojsus/index.php/AMSIL/article/view/14312. Acesso em: 7 may. 2025.