Jean-Paul Watson J. Christopher Beck Adele E. Howe L. Darrell Whitley Problem difficulty for tabu search in job-shop scheduling. 189-217 2003 143 Artif. Intell. 2 http://dx.doi.org/10.1016/S0004-3702(02)00363-6 db/journals/ai/ai143.html#WatsonBHW03