Until now we have been computing the entropy of a single variable. But most of what we will use entropy for involves sequences. For a grammar, for example, we will be computing the entropy of some sequence of words W = {w 1 , w 2 , . . . , w n }. One way to do this is to have a variable that ranges over sequences of words. For example we can compute the entropy of a random variable that ranges over all finite sequences of words of length n in some language L as follows: