Mark de Berg Jit Bose David Bremner William Evans Lata Narayanan 1

This paper addresses the problem of fixed probes; in our setting the locations of the probes must be chosen before the input is examined. In the case of intersection probes, we show that for each natural number n there is a set of n + 1 probe lines that will serve to determine any arrangement of n input lines. We also show that n + 1 is sometimes necessary. In general, we obtain asymptotically tight upper and lower bounds on the maximum number of input lines that are compatible with