Hi Geoffrey, I tried to follow your advice, but by debugging I noticed that he still did not consider taboo the right moves. For not implementing the changes to the solver I modified the data object model. But now I have another problem, I do not understand the log.   Normally when I make a move, the undo move is considered taboo for the next X steps i.e.: -> do a move (CN 16, SR 11) => (CN 16, FR 9) 2010-02-09 15:30:22,700 [main] INFO Step index (29), spend time (32680) taking steps ((CN 16, SR 11) => (CN 16, FR 9)) out of 1800 accepted moves . 2010-02-09 15:30:22,701 [main] INFO New score (-65499.76254006752hard/-126.69878682377347soft) is better then last best score (-76061.73601857488hard/-147.80880935909272soft). Updating best solution and best score. -> evaluating next step the undo move (CN 16, SR 9) => (CN 16, FR 11) is considered taboo 2010-02-09 15:30:22,864 [main] DEBUG Proposed move ((CN 16, SR 9) => (CN 16, FR 11)) is complete taboo. 2010-02-09 15:30:23,746 [main] INFO Step index (30), spend time (33726) taking steps ((CN 57, SR 10) => (CN 57, FR 11)) out of 1799 accepted moves . but often happens that if I make a move the next step make the undo move and then the move is considered taboo: -> do a move (CN 28, SR 18) => (CN 28, FR 12) 2010-02-09 15:30:33,344 [main] INFO Step index (39), spend time (43324) taking steps ((CN 28, SR 18) => (CN 28, FR 12)) out of 1798 accepted moves . 2010-02-09 15:30:33,345 [main] INFO New score (-44072.81924277624hard/-83.90311931887312soft) is better then last best score (-44078.036191138206hard/-83.90311931887312soft). Updating best solution and best score. -> why evaluating the next step the move (CN 28, SR 12)  => (CN 28, SR 18) isn't considered taboo? 2010-02-09 15:30:33,511 [main] DEBUG Proposed move ((CN 16, SR 9) => (CN 16, FR 11)) is complete taboo. 44072 2010-02-09 15:30:33,942 [main] DEBUG Proposed move ((CN 57, SR 11) => (CN 57, FR 10)) is complete taboo. 2010-02-09 15:30:34,420 [main] INFO Step index (40), spend time (44400) taking steps ((CN 28, SR 12) => (CN 28, FR 18)) out of 1798 accepted moves . 2010-02-09 15:30:34,421 [main] INFO New score (-44078.036191138206hard/-83.90311931887312soft) is not better then last best score (-44072.81924277624hard/-83.90311931887312soft). 2010-02-09 15:30:34,587 [main] DEBUG Proposed move ((CN 16, SR 9) => (CN 16, FR 11)) is complete taboo. 2010-02-09 15:30:34,716 [main] DEBUG Proposed move ((CN 28, SR 18) => (CN 28, FR 12)) is complete taboo. 2010-02-09 15:30:35,021 [main] DEBUG Proposed move ((CN 57, SR 11) => (CN 57, FR 10)) is complete taboo. 2010-02-09 15:30:35,487 [main] INFO  Step index (41), time spend (45467) taking step (( CN 27 ,SR 10) => ( CN 27 ,FR 12 )) out of 1797 accepted moves. why this behavior? regards, Marco