On Eigenspaces of the Hecke Algebra with Respect to a Good Maximal Compact Subgroup of ap-Adic Reductive Group. Shin-ichi Kato — 1981 Mathematische Annalen
Spherical Functions and a q-Analogue of Kostant's Weight Multiplicity Formula. Shin-ichi Kato — 1982 Inventiones mathematicae