The 0 on row 1 is the first domino. Once that row is crossed out, the edge 2 window shrinks from five cells to two. Now cells-left equals ghosts-left, so both yellow cells are ghosts. One deduction triggers the next — a chain called propagation. After each move, watch how far the dominoes fall.

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.