To reduce size of the large BDD, different approaches are used – optimal ordering (OBDD), Reduction Operations (ROBDD), Zero-Suppressed BDD (ZBDD), etc. But sometimes, for very large fault trees, even after using of these approaches, it is impossible to build full (exact) BDD and so we should use some Cut-Off. Please, recommend me some approaches or give me some references for BDD Cut-Off. Thanks a lot beforehand. Regards, Sergey.