“…Clearly, us depends only on s and s 0 (and the orientations , 0 ), and sv depends only on s and s 00 (and the orientations , 00 ), which readily implies the lemma. 2 We next x three edge orientations , 0 , 00 , x the point s as de ned above (there are c choices for this point), and construct a matrix M, whose rows correspond to the points s 0 2 S, sorted in increasing order of 1 (s ; s 0 ), as de ned above, and whose columns correspond to the points s 00 2 S, sorted in increasing order of 2 (s ; s 00 ). We put M ij = We remark that more general polygonal 2-center problems can be solved in O(n polylog n) time, using the parametric searching technique 36], as was also done in Section 3.2, for the general rectilinear 4-and 5-center problems.…”