“…For particular functions f (x), d x (x, y), p y (x, y), d y (x, y), a y (y), and φ(t), the generic model (6) reduces to specific models derived in the literature (Forys et al 2006;Galach 2003;Kuznetsov et al 1994;Stepanova 1980;Sotolongo-Costa et al 2003;de Vladar and González 2004). For instance, the model derived in Kuznetsov et al (1994) is obtained by setting…”