My own book may be crap, but I am certain, when such an imbalance in profitability as the one I have just described emerges, between photojournalism and selfies, that it is all over. This is not a critical judgment. I am not saying that the photos of Pol Pot are good and the selfies are bad. I am saying that the one reveals a subject and the other reveals an algorithm, and that when everything in our society is driven and sustained in existence by the latter, it is all over.
Wang tiles (Hao Wang, 1961) are a class of formal systems. They are modelled visually by square tiles with a color on each side. A set of such tiles is selected, and copies of the tiles are arranged side by side with matching colors, without rotating or reflecting them.
The basic question about a set of Wang tiles is whether it can tile the plane or not, i.e., whether an entire infinite plane can be filled this way. The next question is whether this can be done in a periodic pattern.
In 1966, Wang's student Robert Berger solved the problem in the negative. He proved that no algorithm for the problem can exist, by showing how to translate any Turing machine into a set of Wang tiles that tiles the plane if and only if the Turing machine does not halt. The undecidability of the halting problem then implies the undecidability of Wang's tiling problem.
It is related that the bodhisattva Manjusri was once standing at the gate, and seeing him, Shakyamuni Buddha called to him, "Manju, Manju, why don't you come inside the gate?"
Manjusri replied, "I don't see anything outside the gate."
When you once attain true self-realization, these barriers disappear in an instant as though they were nothing but mirages, and you will find that from the very beginning you have always been in a world where there is neither inside nor outside. That is what "gateless" means. Therefore, all koans are impassable barriers for those who are unenlightened, but for the enlightened there is no gate at all. They can come and go quite freely.
One day, as Kyogen was clearing the undergrowth, a pebble bounced off the tip of his broom and resounded against a bamboo tree. Hearing the sound, he suddenly experienced great enlightement. The first stanza of the poem he composed on this occasion is very famous:
One striking sound,
and I have forgotten all I knew.