DOŠLÝ, Ondřej and Roman HILSCHER. A class of Sturm-Liouville difference equations: (non)oscillation constants and property BD. Comput Math. Appl. 2003, vol. 45, No 1, p. 961-981. ISSN 0898-1221.
HILSCHER, Roman. Discrete spectra criteria for certain classes of singular diffferential and difference operators. Computers & mathematics with applications. New York: Pergamon Press, 2001, vol. 42, 3-5, p. 465-476. ISSN 0097-4943.
HILSCHER, Roman. Spectral properties of general self-adjoint, even order differential operators. Mathematica Slovaca. Bratislava: Slovak Academy of Sciences, 2000, vol. 50, No 2, p. 165-186, 21 pp. ISSN 0139-9918.
DOŠLÝ, Ondřej and Roman HILSCHER. Spectral properties of fourth order differential operators. Mathematica Bohemica : časopis pro pěstování matematiky. Praha: Matematický ústav AV ČR, 1997, vol. 122, No 3, p. 153-168. ISSN 0862-7959.