DeRose (1988) developed a quasi-HMM algorithm, including the use of dynamic programming, although computing P(t|w)P(w) instead of P(w|t)P(w). The same year, the probabilistic PARTS tagger of Church 1988 Church , 1989 was probably the first implemented HMM tagger, described correctly in Church (1989), although Church (1988) also described the computation incorrectly as P(t|w)P(w) instead of P(w|t)P(w). Church (p.c.) explained that he had simplified for pedagogical purposes because using the probability P(t|w) made the idea seem more understandable as "storing a lexicon in an almost standard form".