“…There is a big literature, in particular high order methods and three dimensional problems are treated in [2,5,7,8,9,18,22,26,27,29,29,34,35,36,38,40]. There is a classical paper on multi-level analysis for h-version DG methods by Gopalakrishnan and Kanschat [17], and a recent one studying higher order methods by Antonietti and Houston [3] showing a polynomial growth of the condition number in p. We will see that the conditioning is significantly improved by hybridization, namely to a poly-logarithmic growth.…”