E. Meel, David. “MODELS AND THEORIES OF THE MATHEMATICAL UNDERSTANDING: COMPARING PIRIE AND KIEREN’S MODEL OF THE GROWTH OF MATHEMATICAL UNDERSTANDING AND APOS THEORY”. Revista Latinoamericana de Investigación en Matemática Educativa 6, no. 3 (November 30, 2003): 221–278. Accessed August 28, 2026. https://www.relime.org/index.php/relime/article/view/546.