There is much misinformation about what a koan is for- it is never meant to be 'solved'. It is designed to build awareness of incongruity, of a disconnect, of living with contradiction. They were originally used in a quick fire fashion and quickly forgotten or passed on from or handed around in a neutral fashion- otherwise obsession would develop. The only remnant of this is the vague knowledge that a lot of laughing is usually involved- this is the remains of what was used to neutralise obsession. The teacher never required a response from the student- the whole point was for the student to become of aware of ALL his responses.