new book with 60 hard puzzles
In the Netherlands I published a "doeboek" ("activity book") for smarter high school children,
with 60 Calcudoku puzzles in it.This is the page describing the book (via Google translate)order form (in Dutch)
(no problems with writing in English, just about everyone in the Netherlands knows the language). The book costs 7 euros, + 3.95 euros shipping (which may
obviously be more when sent abroad).