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rwst/Even-Integral

Ralf Stephan (direction, review, paper author)

Palomar Registrypalomar/PALOMAR-2026-08-20-000006Sep 3, 2026math.NTscore 0

A Lean 4 / Mathlib development of a paper, which improves on a problem by Dubickas. Dubickas (Glasgow Math. J. 48 (2006), 331–336) splits the reals α > 1 in two: α lies in 𝒵 when some real ξ ≠ 0 makes every integral part ⌊ξαⁿ⌋, n ≥ 1, even, and in 𝒮 otherwise. At α = 3/2 this is Mahler's question, and open; his Problem 5 asks whether 𝒮 has an element greater than 2. This formalization decides 𝒮 versus 𝒵 for every quadratic Pisot number: the golden mean is the only one in 𝒮, so none greater than 2 lies there and Problem 5 loses its whole natural class of candidates, though the problem itself…

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