[1] Graz Univ Technol, Inst Software Technol, A-8010 Graz, Austria
[2] Univ Seville, Dept Matemat Aplicada 2, Seville, Spain
[3] Inst Politecn Nacl, Ctr Invest & Estudios Avanzados, Dept Matemat, Mexico City, DF, Mexico
[4] Univ Chile, DCC, Santiago, Chile
[5] Graz Univ Technol, A-8010 Graz, Austria