R. V. Subramaniyam A. A. Diwan A Counterexample for the Sufficiency of Edge Guards in Star Polygons. 97-99 1991 40 Inf. Process. Lett. 2 db/journals/ipl/ipl40.html#SubramaniyamD91 http://dx.doi.org/10.1016/0020-0190(91)90016-B