Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

One of the well-known problems of classical probability theory is the determination of the set of all extreme points in the convex set of all probability distributions in a product Borel space $\left (X \times Y, \:\:{\cal F} \times {\cal G} \right )$ with fixed marginal distributions $\mu$ and $\nu$ on $\left (X, {\cal F} \right )$ and $\left (Y, {\cal G} \right )$ respectively. Denote this convex set by $C(\mu, \nu).$

When $X = Y = \left \{ 1,2,\ldots,n \right \},$ ${\cal F} = {\cal G}$ is the field of all subsets of $X$ and $\mu = \nu$ is the uniform distribution then the problem is answered by the Birkhoff.

I do not work in probability theory. I have heard that the above result is the 'only' result in this direction. Is it true? Can someone please tell me the present status of the above problem. It is nice, if anybody can point out survey article(s) on this matter.

My motivation is to look at the analogues problem in a quantum set up. Birkhoff's theorem and methods are used in some works regarding quantum channels. Hence I want to know the present status of the problem. Advanced thanks for all the helps.

share|cite|improve this question

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Browse other questions tagged or ask your own question.