Bannai, Eiichi, Etsuko Bannai, Sho Suda, and Hajime Tanaka. “On Relative $t$-Designs in Polynomial Association Schemes”. The Electronic Journal of Combinatorics 22, no. 4 (December 23, 2015): P4.47. Accessed March 27, 2026. https://www.combinatorics.org/ojs/index.php/eljc/article/view/v22i4p47.