In a mass of large bubbles The froth, therefore, though lacking long-range symmetry, nevertheless has very definite rules as to its composition. It is pleasing in appearance because the eye senses this interplay between regularity and irregularity. Structure, Substructure, and Superstructure symmetry
We wonder which is real, he of the picture or he who talks? In the tea room the fear of repetition is a constant presence. The various objects for the decoration of a room should be so selected that no color or design shall be repeated. If you have a living flower, a painting of flowers is not allowable. If you are using a round kettle, the water pitcher should be angular. A cup with a black glaze should not be associated with a tea-caddy of black lacquer. In placing a vase or an incense burner on the tokonoma, care should be taken not to put it in the exact center, lest it divide the space into equal halves. The pillar of the tokonoma should be of a different kind of wood from the other pillars, in order to break any suggestion of monotony in the room. Here again the Japanese method of interior decoration differs from that of the Occident, where we see objects arrayed symmetrically on mantelpieces and elsewhere. In Western houses we are often confronted with what appears to us useless reiteration. We find it trying to talk to a man while his full-length portrait stares at us from behind his back. We wonder which is real, he of the picture or he who talks, and feel a curious conviction that one of them must be fraud. Okakura Kakuzō, The Book of Tea repetitionsymmetry
The problem with trees Many systems are organized hierarchically. The CERNDOC documentation system is an example, as is the Unix file system, and the VMS/HELP system. A tree has the practical advantage of giving every node a unique name. However, it does not allow the system to model the real world. For example, in a hierarchical HELP system such as VMS/HELP, one often gets to a lead on a tree such as: HELP COMPILER SOURCE_FORMAT PRAGMAS DEFAULTS only to find a reference to another leaf: Please see HELP COMPILER COMMAND OPTIONS DEFAULTS PRAGMAS and it is necessary to leave the system and re-enter it. What was needed was a link from one node to another, because in this case the information was not naturally organized into a tree. Tim Berners-Lee, Seeing With Fresh Eyes A City Is Not a Tree hierarchywww