Completion Pool
A cell touching an island one short of its size would finish it — and a finished island is walled in sea on every side. If that walling would trap a 2×2 pool, the cell can't be land after all: it's sea.
How it works
- 1The cell right of the 2 touches only that island, so land there would have to join it — finishing the island at exactly 2.
- 2A finished island is walled in by sea on every side, so the cells above and below the pair, and the one to its right, would all become water.
- 3Together with the two sea cells already in the top-left, that wall makes a 2×2 pool, which is illegal.
- 4So the cell could never have been land: it's sea.
- Sea
- Cells that establish the pattern
- Where the conclusion lands