@book{ Solr-acta42583, title = {On solvability of periodic boundary value problems for second order linear functional differential equations}, series = {Electronic journal of qualitative theory of differential equations}, author = {Bravyi Eugene}, year = {2016}, url = {http://acta.bibl.u-szeged.hu/42583/1/ejqtde_2016_005_001-018.pdf} }