ABSTRACT. Differential search games with simple motions of objects oll an infinite circular cylinder are approached geometrically, using sets whose structure depends on time. Sufficient conditions for detection with the corresponding strategies are given. New kinds of problems are proposed, their connections with the initial parameters are investigated.w Introduction It is generally agreed that the mathematical theory of search was founded in the articles [1][2][3], which stimulated numerous publications discussing diverse search problems (detailed references can be found in [4][5][6]). It should be noted that most of the investigations dealt with search problems in which the searching object possessed sufficiently ample information about the location of the eluding object.The geometric method (the method of tracing areas) used in this work and based on the use of certain auxiliary sets that change in time is one of the approaches that have been developed just recently ([7-11]), although some elements of the geometric approach can be found in [12].
w Statement of the search problemHere we consider the search problem in the following setting. Point objects A (the searching object) and B (the eluding object) move in an arcwise connected set X; their speeds are constant and equal to a and /~ (/~ < a), respectively. The eluding object B is considered detected if its distance from the searching object A is not greater than a certain given positive I. It is assumed that the parameters a, /3 and l and the structure of the "hunting ground" X are known to both objects; in addition, the object B also knows the entire trajectory of the object A and the location of A on this trajectory at any time.The actual problem is to specify (1) sufficient conditions on a, ~, and l that make successful search (detection) feasible; (2) a trajectory such that, moving along it, the searching object A will successfully detect B.Remark. It is convenient to assume that at any moment of time the object A is at the center of a circle of radius l forbidden for B. This circle will be called the control l-circle or just the control circle.w Tracing areaIn [7][8][9][10][11], it was shown that the investigation of search problems in the setting described above quite naturally leads to a class of sets of variable structure containing the control/-circle and free of the eluding object B. These auxiliary sets, called tracing area~ are constructed from a given trajectory of A and combine two components, namely the set of points that the eluding object B has no time to reach at a given moment of time (the af'termath area) and the set of points that B has no time to leave (the no-e~cape area).