Nothing points off the board

The border is the first clue of every puzzle.

A pipe may not point past the edge of the board. That alone fixes many tiles on the border: a corner in a corner of the board, a straight pipe along an edge, a tee with its back to the edge.

How it works

Your turn

Four positions, each needing this lesson’s technique. The pinned tiles are given; turn the free ones until every lamp is lit. Click a tile to turn it, Ctrl+click to turn it back; right click or long press pins it.

Why it works

On a board with edges this is where every game starts: corners and border tiles fix themselves. The next lesson carries that certainty from the border into the middle.