Designs in compact symmetric spaces and applications of great antipodal sets

Abstract

The theory of designs is an important branch of combinatorial mathematics. It is well-known in the theory of designs that a finite subset of a sphere is a tight spherical 1-design if and only if it is a pair of antipodal points. On the other hand, antipodal sets and 2-number for a Riemannian manifold are introduced by B.-Y. Chen and T. Nagano in 1982. An antipodal set is called a great antipodal set if its cardinality is equal to the 2-number. The main purpose of this paper is to provide a survey on important results in compact symmetric spaces with great antipodal sets as the designs. In the last two sections of this paper, we present some important applications of 2-number and great antipodal sets to topology and group theory.