[Submitted on 17 Sep 2022 (v1), last revised 2 Jul 2026 (this version, v2)]

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Abstract:In 2020, Lin and Yu claimed to prove the so-called Lemmens--Seidel conjecture for base size $5$. However, their proof has a gap. In this paper, we prove the conjecture for base size $5$ using the pillar method. We also show that the sets of $57$ equiangular lines with common angle $\arccos(1/5)$ in dimension $18$ found by Greaves et~al. \ in 2021 are indeed counterexamples to one of Lin and Yu's this http URL prove this by answering the question posed by Greaves et~al. \ in 2021 in the this http URL asked whether these sets are contained in the unique set of $276$ equiangular lines with common angle $\arccos(1/5)$ in dimension $23$. Furthermore, we show that these sets are strongly maximal. This gives a negative answer to the question posed by Cao et~al.\ in 2021. They asked whether the unique set of $276$ equiangular lines with common angle $\arccos(1/5)$ in dimension $23$ is the unique strongly maximal set of equiangular lines with common angle $\arccos(1/5)$.

Submission history

From: Kiyoto Yoshino [view email]
[v1] Sat, 17 Sep 2022 10:36:57 UTC (15 KB)
[v2] Thu, 2 Jul 2026 06:20:54 UTC (25 KB)

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