“…Among them, the most interesting one are (for a complete review the reader may refer to Cantarella, de Luca, Di Gangi, & Di Pace, 2013) : Fernandez, Florian, De Cea, and Cabrera (1994); Nagurney, Ramanujam, and Dhanda (1998); Lundqvist and Abrahamsson (1999); May and Milne (2000); De Cea and Fernandez (2001); Clegg, Smith, Xiang, and Yarrow (2001); Yildirim and Hearn (2005); Zhou, Chen, and Wong (2009); D'Acierno, Gallo, and Montella (2006); Meng and Liu (2012). Alternative and interesting approaches are presented by Wong (1998) and Wichiensin, Bell, and Yang (2007).…”