The probability of finding an A B pair is product of the fraction of A and the probability of layer type B following layer type A . Here we have six variables with four independent equations. Therefore, by giving any two variables the complete system is described. This treatment only applies to sequences which are affected by its nearest neighbor. The random case is specified by equal probabilities of any layer being followed by an A which in turn is equal to the amount of layer type A .
P A describes conditions from perfect to random interstratification.
When this term is greater than zero, it provides a description of the nearing-neighbor effects.