Ring is an example of an "infinite" data structure, in a sense that,unlike a finite list, there is always a predecessor and successor toany element in the ring. Therefore, the ring is implemented"recursively", in terms of links. A link is made of a link value and afunction that, when called, generates another link. Function'make-ring' already shows self-infecting traits, in that it generatesa data structure and inserts itself as a part of it.

A single robot, or even a half-dozen of them, can't do everything that emergency personnel might need -- such as collecting air samples, testing for toxic fumes or monitoring a large area to find the wounded. Robots have to do much of this work on their own. Humans usually can't control more than three or four robots at one time