1. CieŚlak, W. and Góźdź, S., Extremal polygons circumscribed an oval,Acta Math. Hung. 54 (1–2) (1989), 63–68.
2. Eggleston, H.G., On triangles circumscribing plane convex sets,J. London Math. Soc. 28 (1953), 36–46.
3. Santalo, L.A., Integral Geometry and Geometric Probability, Addison-Wesley Publishing Company, Inc., 1976.
4. Valentine, F., Convex sets, McGraw-Hill, New York 1964.