Jurek Czyzowicz Eduardo Rivera-Campo Nicola Santoro Jorge Urrutia Joseph Zaks Tight Bounds for the Rectangualr Art Gallery Problem. 105-112 1991 conf/wg/1991 WG db/conf/wg/wg91.html#CzyzowiczRSUZ91 http://dx.doi.org/10.1007/3-540-55121-2_10