“…Arnold et al (2001), and the references cited therein. DG methods are ideally suited for realizing hp-adaptivity for secondorder boundary value problems, an advantage that has been noted early on in the recent development of these methods; see, for example, Baumann & Oden (1999), Rivière et al (1999), Cockburn et al (2000), Perugia & Schötzau (2002), Wihler et al (2003), Houston et al (2002Houston et al ( , 2007Houston et al ( , 2008, Stamm & Wihler (2010) and the references therein. Indeed, working with discontinuous finite element spaces easily facilitates the use of variable polynomial degrees and local mesh refinement techniques on possibly irregularly refined meshes-the two key ingredients for hp-adaptive algorithms.…”