STEFANOVSKI, J., K. TRENCEVSKI, and V. COVACHEV. “CAUCHY PROBLEM AND REDUCTION OF A SYSTEM OF PARTIAL DIFFERENTIAL EQUATIONS”. Tamkang Journal of Mathematics 30, no. 4 (December 1, 1999): 315–329. Accessed January 22, 2025. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/4238.