Gunawan, Hendra, Muhamad Jamaludin, and Mas Daffa Pratamadirdja. “On Birkhoff Angles in Normed Spaces”. Journal of the Indonesian Mathematical Society 27, no. 3 (December 2, 2021): 270–284. Accessed November 21, 2024. https://jims-a.org./index.php/jimsa/article/view/1030.