Pierluigi Crescenzi Paolo Penna Adolfo Piperno Linear area upward drawings of AVL trees. 25-42 1998 9 Comput. Geom. 1-2 db/journals/comgeo/comgeo9.html#CrescenziPP98 http://dx.doi.org/10.1016/S0925-7721(97)00013-8