““‘The six interior sense fields should be understood. The six exterior sense fields should be understood. The six classes of consciousness should be understood. The six classes of contact should be understood. The eighteen mental preoccupations should be understood. The thirty-six positions of sentient beings should be understood. Therein, relying on this, give up that. The Noble One cultivates the establishment of mindfulness in three cases, by virtue of which they are a Teacher worthy to instruct a group. Of all meditation tutors, it is he that is called the supreme guide for those fit for training.’ ”