Let {Xn} (n = 1, 2 , …) be a stochastic process. The random variables comprising it or the process itself will be said to be interchangeable if, for any choice of distinct positive integers i1, i2, H3 … , ik, the joint distribution of
![](//static.cambridge.org/content/id/urn%3Acambridge.org%3Aid%3Aarticle%3AS0008414X00045326/resource/name/S0008414X00045326_eqn1.gif?pub-status=live)
depends merely on k and is independent of the integers i1, i2, … , ik. It was shown by De Finetti (3) that the probability measure for any interchangeable process is a mixture of probability measures of processes each consisting of independent and identically distributed random variables.