@misc{pre-03-xfarbe, author = {A. Preusser}, title = {{XFARBE} - {Fill} Area with Bicubics}, url = {http://www.fhi-berlin.mpg.de/grz/pub/xfarbe_doc.html}, howpublished = {Online document}, year = 2003, comment = {We used this software to generate a figure for the Affine Arithmetic monograph, illustrating level sets of a bivariate function.}, altkeys = {xfarbe} }