“2 × 9 = 81 Conversely and 9 × 9 = 18 conversely” Mathematic Play of 9- Year-Old, the Copyright and the Civil Law”. Discourse of Law and Administration, no. 1 (March 4, 2024). Accessed December 14, 2025. https://www.dyskurs.inp.uz.zgora.pl/index.php/DPiA/article/view/414.