C. Cortés José Miguel Díaz-Báñez P. Pérez-Lantero Carlos Seara Jorge Urrutia Inmaculada Ventura Bichromatic separability with two boxes: A general approach. 79-88 2009 64 J. Algorithms 2-3 http://dx.doi.org/10.1016/j.jalgor.2009.01.001 db/journals/jal/jal64.html#CortesDPSUV09