Christopher Lusena Judy Goldsmith Martin Mundhenk Nonapproximability Results for Partially Observable Markov Decision Processes. 83-103 2001 14 J. Artif. Intell. Res. (JAIR) http://www.cs.washington.edu/research/jair/abstracts/lusena01a.html db/journals/jair/jair14.html#LusenaGM01