DIRECT AND INDIRECT METHODS OF PROOF. THE LEHMUS-STEINER THEOREM. Annual of Sofia University St. Kliment Ohridski. Faculty of Mathematics and Informatics, [S. l.], v. 103, p. 105–121, 2016. Disponível em: https://annual.uni-sofia.bg/index.php/fmi/article/view/59. Acesso em: 15 dec. 2025.