SEPTIATI, Ety; HILTRIMARTIN, Cecil; HARTONO, Yusuf. Proof -Based Learning Design Using APOS Theory on Triangle Inequality Theorem Material. Journal of Education and Learning Mathematics Research (JELMaR), [S. l.], v. 4, n. 2, p. 192–203, 2023. DOI: 10.37303/jelmar.v4i2.163. Disponível em: https://jelmar.wisnuwardhana.ac.id/index.php/jelmar/article/view/163. Acesso em: 25 aug. 2026.