Modelingtasks,suchassurfacedeformationandediting,canbeanalyzedbyobservingthelocalbehaviorofthesurface.Wearguethatdefiningamodelingoperationbyaskingforrigidityofthelocaltransformationsisusefulinvarioussettings.Suchformulationleadstoanon-linear,yetconceptuallysimpleenergyformulation,wh