Lactoedron
The first description of the lactoedron was given in 1956 by Grossman, but it is known that its existence had been conjectured by Hilbert, as mentioned in one of his correspondences with Klein. To date, only parametric representations are available and the search for an implicit equation of this surface (of sixth degree, like that of the Boy) mobilizes a small group of specialists. The images that can be found on this site come from recent results by Iéronimus Holstein and Miroslav Milka.