'In Zen, practitioners use kung-an (koans) as subjects for meditation until their mind comes to awakening. There is a big difference between a kung-an and a math problem the solution of the math problem is included in the problem itself, while the response to the kung-an lies in the life of the practitioner. The kung-an is a useful instrument in the work of awakening, just as a pick is a useful instrument in working on the ground. What is accomplished from working on the ground depends on the person doing the work and not just on the pick. The kung-an is not an enigma to resolve this is why we cannot say that it is a theme or subject of meditation.