Prime Implicants of Noncoherent Fault Trees

The discussion prompted by a Kumamoto & Henley paper is analyzed and the central issues are set forth. Results of the SETS program are used to clarify some misunderstandings and to show that it can be used to obtain quickly all of the results presented by Kumamoto & Henley. A special class of noncoherent trees is identified on which the standard algorithm for coherent trees will always work.