Brun, Viggo, and Finn F. Knudsen. “On the Possibility of Finding Certain Criteria for the Irrationality of a Number Defined As a Limit of a Sequence of Rational Numbers”. MATHEMATICA SCANDINAVICA 31 (June 1, 1972): 231–236. Accessed November 24, 2024. https://www.mscand.dk/article/view/11429.