Peter Boyvalenkov, Oleg Mushkarov, emil Kolev & Nikolai Nikolov books & textbook
Bulgarian Mathematical Competitions 20032006
Peter Boyvalenkov, Oleg Mushkarov, emil Kolev & Nikolai Nikolov
Levant Books /2014T Paperback
isbn-10: 9380663935 / isbn-13: 9789380663937