The question of gentrification The question of gentrification is made complex by the fact that the urban qualities it produces—lively street life, profuse commerce, preservation and upgrading of old buildings—are highly desirable, the substrate of urbanity. The problem with gentrification is with its particulars and with its effects. Gentrification suppresses reciprocity by its narrowed scripting of formal and social behavior, by turning neighborhoods into Disneylands or Colonial Williamsburgs, where residents become cast members and the rituals of everyday life become spectacle or food for consumption. Michael Sorkin, 20 Minutes in Manhattan gentrificationurbanism
Wang tiles 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. Wikipedia en.wikipedia.org Truchet TilesThe Tiling Patterns of Sebastien Truchet and the Topology of Structural Hierarchy mathalgorithms