Non-Desarguesian plane
Projective plane not satisfying Desargues' theorem / From Wikipedia, the free encyclopedia
In mathematics, a non-Desarguesian plane is a projective plane that does not satisfy Desargues' theorem (named after Girard Desargues), or in other words a plane that is not a Desarguesian plane. The theorem of Desargues is true in all projective spaces of dimension not 2;[1] in other words, the only projective spaces of dimension not equal to 2 are the classical projective geometries over a field (or division ring). However, David Hilbert found that some projective planes do not satisfy it.[2][3] The current state of knowledge of these examples is not complete.[4]