2 To calculate the prior, we first use Bayes rule to rewrite it as Recall that at this point, i and j do not refer to index positions in the actual string but rather serve to identify the substring w j i of interest.
p (w j i ) denotes the probability that at an arbitrary point in  There are at least j words an arbitrary sentence, the next j − i words will be w j i , and p (X k≥j i ) denotes the probability that an arbitrary point in an arbitrary sentence will be the left edge of a category X that spans at least j − i words.