arXiv subjects
Publications and source records attributed to Leonid A. Levin.
This is a 1971 dissertation. Only its extended abstract was published at the time. While some results appeared in other publications, a number of details remained unpublished and may still have relevance.
We study the minimal complexity of tilings of a plane with a given tile set. We note that every tile set admits either no tiling or some tiling with O(n) Kolmogorov complexity of its n-by-n squares. We construct tile sets for which this bound is tight: all n-by-n squares in all tilings have complexity at least n. This adds a quantitative angle to classical results on non-recursivity of tilings -- that we also develop in terms of Turing degrees of unsolvability. Keywords: Tilings, Kolmogorov complexity, recursion theory
[Gacs, Kurdiumov, Levin, 78] proposed simple one-dimensional cellular automata with 2 states. In an infinite array they are self-stabilizing: if all but a finite minority of automata are in the same state, the minority states disappear. Implicit in the paper was a stronger result that a sufficiently small minority of states vanish even in a finite circular array. The following note makes this strengthening explicit.
Classical results on aperiodic tilings are rather complicated and not widely understood. Below, an alternative approach is discussed in hope to provide additional intuition not apparent in classical works.
Byzantine Agreement introduced in [Pease, Shostak, Lamport, 80] is a widely used building block of reliable distributed protocols. It simulates broadcast despite the presence of faulty parties within the network, traditionally using only private unicast links. Under such conditions, Byzantine Agreement requires more than 2/3 of the parties to be compliant. [Fitzi, Maurer, 00], constructed a Byzantine Agreement protocol for any compliant majority based on an additional primitive allowing transmission to any two parties simultaneously. They proposed a problem of generalizing these results to wider channels and fewer compliant parties. We prove that 2f < kh condition is necessary and sufficient for implementing broadcast with h compliant and f faulty parties using k-cast channels.
The existence of one-way functions is arguably the most important problem in computer theory. The article discusses and refines a number of concepts relevant to this problem. For instance, it gives the first combinatorial complete owf, i.e., a function which is one-way if any function is. There are surprisingly many subtleties in basic definitions. Some of these subtleties are discussed or hinted at in the literature and some are overlooked. Here, a unified approach is attempted.