“…Just as a short reference to some of the most interesting works, it is worth mentioning the old but excellent survey edited by Armstrong and Vickerman (1995). More recently, the books edited by Cuadrado-Roura and Parellada (2002) and Fingleton (2003), reviews as Magrini (2004), and papers such as those of López-Bazo et al (1999), Badinger et al (2004), Miller and Genc (2005), Fingleton and López-Bazo (2006), Meliciani (2006), Arbia et al (2008), Fischer and Stumpner (2008), and Mora (2008) are very good references.…”