On the Union of kappa-Round Objects in Three and Four Dimensions.

Boris Aronov Alon Efrat Vladlen Koltun Micha Sharir On the Union of kappa-Round Objects in Three and Four Dimensions. 511-526 2006 36 Discrete & Computational Geometry 4 http://dx.doi.org/10.1007/s00454-006-1263-x db/journals/dcg/dcg36.html#AronovEKS06