1. B. Grünbaum, Solution of a problem (P 77) of Leo Moser,Canad. Math. Bull. 7 (1964), 477–478.
2. Pure and applied mathematics;B. Grünbaum,1967
3. S. Roberts, On the figures formed by the intercepts of a system of straight lines in a plane, and on analogous relations in space of three dimension,Proc. London Math. Soc. 19 (1887–1888), 405–422.
4. R. K. Guy, Unsolved combinatorial problems,Combinatorial Mathematics and its Applications (Proc. Conf., Oxford, 1969), ed by D. J. A. Welsh, Academic Press, London-New York, 1971, 121–127. (MR 43 # 3126)Zbl 221. 05003