If M = N , the PLI model likelihood, P (L|W), can be expressed in the following form: where P (l i |w i ) is the likelihood of the ith word, w i , generating the ith PLI, l i .
since each word is represented by a unique PLI (the initial letter) in this work, the PLI model score is given by if N = M , insertions and deletions have to be taken into consideration: where represents an empty token.