Fences: walls that solve the puzzle for you
A dark bar between two cells is a fence. Threads can’t pass it — they go around. Every other rule stays the same: matching buttons, no crossing, the whole cloth covered.
At first fences look like an extra obstacle. In practice they help: a fence removes one exit from each of the two cells it separates. Fewer exits mean fewer options, and fewer options mean forced moves.
A fence turns a cell into an edge
Look at any cell and count the ways out: up, down, left, right, minus the board edge, minus fences. A thread that passes through a cell (not one that starts there) needs exactly two of those exits.
- Two exits left, on opposite sides — a corridor. Whatever thread passes here goes straight through.
- Two exits left, on adjacent sides — a corner. The thread passing here has to turn.
- One exit left — only a button can sit here: a thread can’t pass through a cell with one way in. If such a cell looks empty, look again — you’ve misread a fence.
In the picture both highlighted cells are decided before you draw anything. The corridor is crossed from top to bottom. The corner connects the cell above it with the cell to its left. Now only one thread can reach both — and the whole board falls into place.
Fences next to the edge
The strongest fences touch the border. A fence one cell away from the edge, running along it, builds a one-cell-wide lane. Such a lane fills in one go: the thread enters at one end and leaves at the other. Treat it like a stretch of edge and solve it first, the same way you would start from corners in classic levels (see /guides/corners-and-edges/).
Fences that form a pocket — three sides closed — are the other gift. A cell like that has one way in, so it must hold a button, or the thread entering it would have nowhere to go. That’s the same pocket logic as in /guides/dead-ends-and-pockets/, only the board draws the walls for you.
Where to practise
A routine for every fence level
- Scan the board for fences and mark in your head every cell with only two exits.
- Draw the corridors and corners that are already decided — they are free moves.
- Check the cells next to the new threads: a placed thread takes away exits just like a fence does.
- Only then go back to the usual edge and corner reasoning for the rest of the board.
The Fences set goes from small 5×5 boards with a few fences to 7×7 levels with long fence lines and only two threads. In the small and mean set fences mix with other rules. With two threads on a big board the fences are the main clue — count exits cell by cell.