Rémi Allègre Eric Galin Raphaëlle Chaine Samir Akkouche The HybridTree: A Hybrid Constructive Shape Representation for Free-Form Modeling. 60-89 2008 Heterogeneous Objects Modelling and Applications http://dx.doi.org/10.1007/978-3-540-68443-5_3 series/lncs/4889 db/series/lncs/lncs4889.html#AllegreGCA08