On bounded solutions to systems of linear functional-differential equations. Hakl, R. — 1999 Georgian Mathematical Journal
On nonnegative bounded solutions to systems of linear functional differential equations. Hakl, R. — 2000 Memoirs on Differential Equations and Mathematical Physics
On a boundary value problem for scalar linear functional differential equations. Hakl, R.; Lomtatidze, A.; Stavroulakis, I.P. — 2004 Abstract and Applied Analysis
Solvability and the unique solvability of a periodic type boundary value problem for first order scalar functional differential equations. Hakl, R.; Lomtatidze, A.; Šremr, J. — 2002 Georgian Mathematical Journal