Institution: | 1. Dept. of Math. and C. S., University of Maribor, Maribor, Slovenia;2. Dept. of Math., Louisiana State University, Baton Rouge, USA;3. Dept. of Comb. & Opt., University of Waterloo, Waterloo, Canada;4. Instituto de Fisica, Universidad Autonoma de San Luis Potosi, San Luis Potosi, Mexico |