Author/Authors :
Acu, Mugur Department of Mathematics and Informatics - Faculty of Sciences -"Lucian Blaga" University, Sibiu, Romania , Owa, Shigeyoshi Department of Mathematics - Faculty of Education - Yamato University, Katayama, Suita, Osaka, Japan , Diaconu, Radu Department of Mathematics and Informatics - Faculty of Sciences -"Lucian Blaga" University, Sibiu, Romania