“…The published papers of which I am aware are Hong (2007Hong ( , 2013, Liebowitz (2006Liebowitz ( , 2008, Michel (2006), Peitz and Waelbroeck (2004), Rob and Waldfogel (2006), Waldfogel (2010) and Zentner (2005Zentner ( , 2006. Two unpublished papers of seemingly similar quality to those that are published are Blackburn (2004) and Zentner (2009).…”