Abstract
We discuss a way of choosing subsequences (selection rule) from binary one-sided infinite sequences such that whether the i-th place is chosen or not is decided by the information before it. It is realized by a countable automaton with input {0, 1} in a way that the i-th place is chosen if and only if the finite subsequence from the beginning to the (i - 1)-place is accepted by the automaton. We characterize selection rules which preserve normality, that is, the subsequence of a normal number chosen by it is always a normal number if the set of chosen places has a positive lower density. Our result is a common generalization of known results for special automata.
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Wang, X., Kamae, T. Selection rules preserving normality. Isr. J. Math. 232, 427–442 (2019). https://doi.org/10.1007/s11856-019-1879-1
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DOI: https://doi.org/10.1007/s11856-019-1879-1