1. Fujiwara, M.: Ein Satz über convexe geschlossene Kurven. Sci. Rept. Tohoku Univ.9, 289?294 (1920)
2. Hombu, H.: Notes on closed convex curves. Tohoku Math. J.33, 72?77 (1930)
3. Kojima, T.: On the curvature of the closed convex curve. Tohoku Math. J.21, 15?20 (1922)
4. Kubota, T.: Notes on closed convex curves. Tohoku Math. J.21, 21?23 (1922)
5. Peterson, B.: Do self-intersections characterize curves of constant width? Amer. Math. Monthly79, 505?506 (1972)