The Lemmens-Seidel conjecture and forbidden subgraphs

Meng Yue Cao, Jack H. Koolen, Yen Chi Roger Lin, Wei Hsuan Yu

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


In this paper we show that the conjecture of Lemmens and Seidel of 1973 for systems of equiangular lines with common angle arccos⁡(1/5) is true. Our main tool is forbidden subgraphs for smallest Seidel eigenvalue −5.

Original languageEnglish
Article number105538
JournalJournal of Combinatorial Theory. Series A
StatePublished - Jan 2022


  • Equiangular lines
  • Forbidden subgraphs
  • Pillar method
  • Seidel matrices


Dive into the research topics of 'The Lemmens-Seidel conjecture and forbidden subgraphs'. Together they form a unique fingerprint.

Cite this