Pasch's theorem

Etymology
Stated in 1882 by the German mathematician.

Proper noun

 * 1)  A result in plane geometry which cannot be derived from Euclid's postulates. It states that, given points a, b, c, and d on a line, if it is known that the points are ordered as (a, b, c) and (b, c, d), then it is also true that (a, b, d).