ISBN 1698909071 books & textbook
David Karn Sudoku Variations – Medium to Hard Vol 1: 90 Large Print Puzzles – 9 Sudoku Variants: X, Hyper, Twins, Triathlon A+B, Marathon, Samurai, 12x12, 16x16 – 16-24 pt font size, 8.5x11" format
Independently published /2019-10-10 Paperback / 138 Pages
isbn-10: 1698909071 / isbn-13: 9781698909073
