When a clue has done its job, erase it in your head. The 1 in the picture found its ghost and its window is crossed out — it has nothing more to say. What remains is only the small puzzle inside the blue frames. Shrinking a problem by deleting the finished parts is called reduction. The more you erase… the more restful the board.

In the app, one new tip arrives for each day you play.

▶ Try 50 rounds in your browser A free demo, no install. All 2,000 rounds are in the app.