Forbidden substrings, Kolmogorov complexity and almost periodic sequences

Abstract

Assume that for some α < 1 and for all nutural n a set F n of at most 2αn "forbidden" binary strings of length n is fixed. Then there exists an infinite binary sequence ω that does not have (long) forbidden substrings. We prove this combinatorial statement by translating it into a statement about Kolmogorov complexity and compare this proofl with a combinatorial one based on Laslo Lovasz local lemma. Then we construct an almost periodic sequence with the same property (thus combines the results from [1] and [2]). Both the combinatorial proof and Kolmogorov complexity argument can be generalized to the multidimensional case. © Springer-Verlag Berlin Heidelberg 2006.