Hakl, R.; Lomtatidze, A.; Šremr, J.
(Нелінійні коливання, 2002)
Nonimprovable sufficient conditions are established for unique solvability of the boundary-value problem u`(t) = l(u)(t) + q(t), u(a) = λu(b) + c,
as well as for nonnegativeness of its solution, where l : C([a, b]; R) → ...