Derek Holton's problem solving series.
Holton, Derek.
Mathematical Association.
Leicester : Mathematical Association,
c1988-c1989.
No. 1. How to -- no. 2. Combinatorics 1 -- no. 3. Graph theory -- no. 4. Number theory -- no. 5. Geometry 1 -- no. 6. -- Proof -- no. 7. Geometry 2 -- no. 8. IMO problems 1 -- no. 9. Combinatorics 2 -- no. 10. Geometry 3.