Past exam of the mathematics course of the University of Cambridge 2023 iii Paper 109 3 iii Solution 2026-09-28
Yes. For every prime power , a finite projective plane of order haspoints and the same number of lines; every two lines meet in exactly one point, and the intersection of all lines is empty. Its lines therefore form one required family on points. The near-pencil from part (ii) is another. They are non-isomorphic because every projective-plane line has size , whereas the near-pencil has a member of size . There are infinitely many prime powers, so infinitely many such .