 However, there are some difficulties with this account of conditional probability. Kolmogorov notes that if the original probability space is the uniform distribution of points on a sphere, and if \(B\) ranges over the set of longitudes (great circles through the poles), then probability conditional on a line of longitude will not be uniform, but instead will be concentrated near the equator. (This fact is known as the “Borel paradox”, because Emile Borel investigated it even before Kolmogorov’s work.) Since every great circle on a sphere can be viewed as a line of longitude with an appropriate choice of pole, this makes the probability conditional on an event depend not only on which event was chosen, but also which family of alternatives it is contrasted with. (We can view each great circle as a longitudinal line through multiple different poles, each of which disagrees about where the equator is.)