Bart Kuijpers Walied Othman An analytic solution to the alibi query in the bead model for moving object data. 2007 Constraint Databases, Geometric Elimination and Geographic Information Systems http://drops.dagstuhl.de/opus/volltexte/2007/1286 conf/dagstuhl/2007P7212 db/conf/dagstuhl/P7212.html#KuijpersO07