Nurkanović M, Nurkanović Z. Birkhoff Normal Forms, Kam Theory, Periodicity and Symmetries for Certain Rational Difference Equation With Cubic Terms. sjm [Internet]. 2024 May 30 [cited 2024 Oct. 15];12(2):217-31. Available from: https://sjm.anubih.ba/index.php/sjm/article/view/190