Accumulation-point conjecture for quotient values of binary sequences

Let u=(un)nN{\bf u}=(u_n)_{n\in\mathbb{N}} be a binary sequence that is not eventually periodic. Suppose that the set of return lengths R(u)\mathcal{R}(\mathbf{u}) is finite, and that

{nN:un=0, un+1=un+2=un+3=1}\{n\in\mathbb{N}: u_n=0,\ u_{n+1}=u_{n+2}=u_{n+3}=1\}

is infinite. Let ff be the sequence defined by the paper's equation for f(n)f(n), and let V(f)\mathcal{V}(f) denote its set of quotient values. Accumulation-point conjecture. For almost all pairs (a,b)(a,b) in the sense of asymptotic density, the set V(f)\mathcal{V}(f) has infinitely many accumulation points. More precisely, its set of accumulation points in R{}\mathbb{R}\cup\{\infty\} is homeomorphic either to a union of the Cantor set and a finite set or to the whole set R{}\mathbb{R}\cup\{\infty\}. The conjecture concerns the structure of quotient values generated by non-eventually-periodic binary sequences; the asserted almost-everywhere conclusion and the alternatives for the accumulation set remain unproved in the supplied text.

Sources & referencesView supporting material

Primary source

Piotr Miska, Bartosz Sobolewski and Maciej Ulas, “Binary sequences meet the Fibonacci sequence”, arXiv:2412.11319 (2025).

Additional references

7 papers in this index state this conjecture (2001–2024). The statement above is taken from the most recent of them; the others are arXiv:2402.15369, arXiv:2001.08923, arXiv:1106.0017, arXiv:0805.0756, arXiv:0705.1210, arXiv:math/0104251.

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