Almeida, Cesário, et al. “Study of the Cognitive Structure of Portuguese Students in Years 9 (14-15 Year-Olds) and 12 (17-18 Year-Olds) Concerning the Notion of Probability: A Contribution of Theories of Nuclear Concepts and Threshold Concepts”. Revista Latinoamericana de Investigación en Matemática Educativa, vol. 20, no. 1, Mar. 2017, pp. 9-38, https://doi.org/10.12802/relime.17.2011.