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.
In real life, what significant change does occur if children are transferred from a lively city street to the usual park or to the usual public or project playground?
In most cases (not all, fortunately), the most significant change is this: The children have moved from under the eyes of a high numerical ratio of adults, into a place where the ratio of adults is low or even nil. To think this represents an improvement in city child rearing is pure daydreaming.