Six rules cover every square this site can work out. Two of them do almost all of it.
| Rule | Share of steps |
|---|---|
| Line finished Every block in this line is already placed, so what is left must be empty — or the other way round. | 55% |
| Overlap Push the blocks as far left as they go, then as far right; wherever a block lands both times, it is filled. | 42.8% |
| Block finished This run of filled squares is already as long as any block that could sit here, so both ends are empty. | 1.2% |
| Gap too small This gap is shorter than the smallest block left, so nothing fits and all of it is empty. | 0.3% |
| Out of reach No block can stretch this far, wherever it starts, so this square is empty. | 0.7% |
| Compare every arrangement None of the shorter rules apply, so every legal arrangement of this line is compared and the squares they agree on are settled. | — |