1. McMullen, P.,Konvexe Körper Probleme, Oberwolfach, May 1978.
2. Rogers, C.A., ?An Equi-chordal Problem? (to appear inGeom. Ded.).
3. Funk, P., ?On a Geometrical Application of Abel's Equation?,Math. Annal. 77, 129 (1915).
4. Whittaker, F. T., and Watson, G. N.,Modern Analysis, C.U.P. (1929), p. 229.