Given an elliptic quadric K of PG(3, q), q odd, suppose that F = (C, , c c1,+3,,*1 2 ,.-*, is a chain of circles on K. Let Pi be the plane of Ci and let Xi be the pole of Pi with respect to K. Then the set F* = {X,, X2 ,-.., Xc4+3j,z} has the properties (i) each line XiXj (i #j), is external to K, (ii) no three points of F* are collinear, and (iii) no… (More)