 Class4 deserves special attention. If we observe the universe generated by Rule 110 we see regular patterns (although not as regular as in Rule 108) as well as some chaotic behavior (although not as noisy as in Rule 90). Now the basic feature a CA needs to perform computations is the capacity of its transition rule of producing “particle-like persistent propagating patterns” (Ilachinski 2001: 89), that is, localized, stable, but non-periodic configurations of groups of cells, sometimes called solitons in the literature, that can preserve their shape. These configurations can be seen as encoding packets of information, preserving them through time, and moving them from one place to another: information can propagate in time and space without undergoing important decay. The amount of unpredictability in the behavior of Class4 rules also hints at computationally interesting features: by the Halting Theorem (see section in entry on  Turing machines),  it is a key feature of universal computation that one cannot in principle predict whether a given computation will halt given a certain input. These insights led Wolfram to conjecture that Class4 CA were (the only ones) capable of universal computation. Intuitively, if we interpret the initial configuration of a Class4 CA as its input data, a universal Class4 CA can evaluate any effectively computable function and emulate a universal Turing machine. As we mentioned above, Rule 110 was indeed proved to be computationally universal.