[1]
Kelevedjiev, P. and Popivanov, N. 2002. EXISTENCE OF SOLUTIONS OF BOUNDARY VALUE PROBLEMS FOR THE EQUATION $f(t,x,x’,x’’) = 0$ WITH FULLY NONLINEAR BOUNDARY CONDITIONS.
Ann. Sofia Univ. Fac. Math. and Inf
. 94, (Dec. 2002), 55–70.