When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
In 2010 I bought a book of Sudoku puzzles in an airport while waiting for my flight. Within a year I was solving every puzzle. Then I bought a book of difficult puzzles, and I was unable to solve them.
When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.