@book{ Solr-acta42221, title = {Existence of solutions for a nonlinear fractional order differential equation}, series = {Electronic journal of qualitative theory of differential equations}, author = {Kaufmann Eric R.}, year = {2009}, url = {http://acta.bibl.u-szeged.hu/42221/1/ejqtde_2009_071_001-009.pdf} }