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arXiv · 2511.20047

Non-dissective coverings by planks

Andrey Kupavskii·Janos Pach
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Abstract

A plank is the part of space between two parallel planes. The following open problem, posed 45 years ago, can be viwed as the converse of Tarski's plank problem (Bang's theorem): Is it true that if the total width of a collection of planks is sufficiently large, then the planks can be individually translated to cover a unit ball $B$? A translative covering of $B$ by planks is said to be non-dissective if the planks can be added one by one, in some order, such that the uncovered part remains connected at each step, and is empty at the end. Improving a classical result of Groemer, we show that every set of $C/\epsilon^{7/4}$ planks of width $\epsilon$ admits a non-dissective translative covering of $B$, provided $C$ is large enough. Our proof yields a low-complexity algorithm. We also establish the first nontrivial lower bound of $c/\epsilon^{4/3}$ for this quantity.

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Andrey Kupavskii, Janos Pach. 2025-11-25. Non-dissective coverings by planks. https://arxiv.org/abs/2511.20047

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