1. Burnside, W.: Theory of groups of finite Order, Chapt. XVII. Cambridge 1911.
2. Kuniyoshi, H.: On purely transcendency of a certain field. Tôhoku Math. J.6, 101?108 (1955).
3. Kuniyoshi, H.: Certain subfields of rational function fields. Proc. Intern. Symp. on alg. Number Theory, 241?243, Tokyo-Nikko 1955.
4. Masuda, K.: On a problem of Chevalley. Nagoya Math. J.8, 59?63 (1955).
5. Morikawa, H.: On the invariants of finite nilpotent groups. Osaka Math. J.10, 53?56.