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A note on the affine-invariant plank problem
Metric Geometry · Submitted 2 Apr 2016
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim In this note we give a short proof of this conjecture under the assumption that, for every $m$ with $1 \leq m \leq k$, $ C \setminus \bigcup_{i = 1}^m P_i $ is a convex set.
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Suppose that $C$ is a bounded, convex subset of $\mathbb{R}^n$, and that $P_1, \dots, P_k$ are planks which cover $C$ in respective directions $v_1, \dots, v_k$ and with widths $w_1, \dots, w_k$. In 1951, Bang conjectured that the sum of relative widths $$\sum_{i=1}^k \frac{w_i}{w_{v_i}(C)} \geq 1, $$ generalizing a previous conjecture of Tarski. Here, $w_{v_i}(C)$ is the width of $C$ in the direction $v_i$. In this note we give a short proof of this conjecture under the assumption that, for every $m$ with $1 \leq m \leq k$, $ C \setminus \bigcup_{i = 1}^m P_i $ is a convex set. In addition, we prove that if the projection of $C$ onto the vector space spanned by the normal vectors of the planks has dimension $d$, then the above sum of relative widths is at least $1/d$.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Suppose that $C$ is a bounded, convex subset of $\mathbb{R}^n$, and that $P_1, \dots, P_k$ are planks which cover $C$ in respective directions $v_1, \dots, v_k$ and with widths $w_1, \dots, w_k$. | background 1.00 | 0.08 | 0.02 | asserted 0.72 |
| s1 | In 1951, Bang conjectured that the sum of relative widths $$\sum_{i=1}^k \frac{w_i}{w_{v_i}(C)} \geq 1, $$ generalizing a previous conjecture of Tarski. | background 1.00 | 0.03 | 0.11 | speculative 0.66 |
| s2 | Here, $w_{v_i}(C)$ is the width of $C$ in the direction $v_i$. | background 0.98 | 0.09 | 0.02 | asserted 0.95 |
| s3 | In this note we give a short proof of this conjecture under the assumption that, for every $m$ with $1 \leq m \leq k$, $ C \setminus \bigcup_{i = 1}^m P_i $ is a convex set. | contribution 0.70 | 0.97 | 0.54 | asserted 1.00 |
| s4 | In addition, we prove that if the projection of $C$ onto the vector space spanned by the normal vectors of the planks has dimension $d$, then the above sum of relative widths is at least $1/d$. | result 0.94 | 0.95 | 0.27 | asserted 1.00 |
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Original abstract
Suppose that $C$ is a bounded, convex subset of $\mathbb{R}^n$, and that $P_1, \dots, P_k$ are planks which cover $C$ in respective directions $v_1, \dots, v_k$ and with widths $w_1, \dots, w_k$. In 1951, Bang conjectured that the sum of relative widths $$\sum_{i=1}^k \frac{w_i}{w_{v_i}(C)} \geq 1, $$ generalizing a previous conjecture of Tarski. Here, $w_{v_i}(C)$ is the width of $C$ in the direction $v_i$. In this note we give a short proof of this conjecture under the assumption that, for every $m$ with $1 \leq m \leq k$, $ C \setminus \bigcup_{i = 1}^m P_i $ is a convex set. In addition, we prove that if the projection of $C$ onto the vector space spanned by the normal vectors of the planks has dimension $d$, then the above sum of relative widths is at least $1/d$.
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