“…, (X n , Y n ). This nonparametric estimation problem has already been considered in several studies; see, e.g., Ahmad (1995), Sköld (1999), Cristóbal and Alcalá (2000), Wu (2000), Cristóbal and Alcalá (2001), Cristóbal et al (2004), Ojeda et al (2007), Ojeda-Cabrera and Van Keilegom (2009), and Chaubey et al (2012). It has potential applications in biology, economics and many other fields (see, e.g., the previous references and Patil and Taillie, 1989).…”