“EXISTENCE OF SOLUTIONS OF BOUNDARY VALUE PROBLEMS FOR THE EQUATION $f(t,x,x’,x’’) = 0$ WITH FULLY NONLINEAR BOUNDARY CONDITIONS” (2002) Annual of Sofia University St. Kliment Ohridski. Faculty of Mathematics and Informatics, 94, pp. 55–70. Available at: https://annual.uni-sofia.bg/index.php/fmi/article/view/190 (Accessed: 14 December 2025).