 According to Hakuin (1685–1768), who systematized kōans, there are formally seventeen hundred cases of kōans, and if sub-questions are added to them, a total number of cases comprising the system would be roughly three thousand. The Zen practitioner of the Rinzai school is required to pass them all in a private consultation with a Zen master who checks the practitioner’s state of mind before he or she is granted a seal of transmission. This transmission is said to occur “only from a Buddha to a[nother] Buddha” (yuibutsu yobutsu).