Institution: | a Department of Computer Science, University of North Texas, P.O. Box 13886, Denton, TX 76203-3886, USA b Department of Computer Science, Loughborough University, Loughborough, LE11 3TU, UK c Department of Mathematics, University of South Carolina, Columbia, SC 29208, USA d Institute of Mathematics, Slovak Academy of Sciences, Dúbravská 9, 841 04 Bratislava, Slovak Republic |