Luiz Velho 0001 Denis Zorin 397-427 2001 18 Comput. Aided Geom. Des. 5 https://doi.org/10.1016/S0167-8396(01)00038-3 https://www.wikidata.org/entity/Q127571371 db/journals/cagd/cagd18.html#VelhoZ01