If you are reading this article, you have probably already mastered the basic "simply by logic" methods up to Medium
and you would like to extend your arsenal of solving strategies. In the "Hard" category we introduce the "wing" strategies
X-Wing, Y-Wing, Swordfish and XYZ-Wing. We also gently
start with the simplest colouring strategy Singles's Chains. Most strategies in the Extreme and
Impossible categories cleverly extend the ideas we introduce here. It is fair to say that if
you master these 5 methods, you should be on a good path to mastering any other solving strategy on our website.
Hard boards are twice more common than Medium boards. A Hard board includes all previously mentioned strategies in addition the new ones. We make sure to have a various selection of all methods up to and including the "Hard" category in each board.