Knudsen, Birgit, Martin H. Fischer, Anne Henning, and Gisa Aschersleben. “The Development of Arabic Digit Knowledge in 4- to 7-Year-Old Children”. Journal of Numerical Cognition 1, no. 1 (October 29, 2015): 21-37. Accessed May 28, 2022. https://jnc.psychopen.eu/index.php/jnc/article/view/5675.