@article{ Solr-acta16019, title = {Double cosine series with nonnegative coefficients}, series = {Acta scientiarum mathematicarum}, author = {Fülöp Vanda}, year = {2004}, url = {http://acta.bibl.u-szeged.hu/16019/1/math_070_numb_001_002_091-100.pdf} }