Two lamps never face each other
Two lamps joined to each other would be cut off from the pump.
A lamp is the end of a pipe. If two lamps next to each other pointed at each other, they would make a network of two tiles with no pump. So a lamp beside another lamp must point some other way.
How it works
The tiles around are fixed as far as the edges and the neighbours go.
Step 1 of 4
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.
Exercise 1 of 4
Turn the free tiles so that every lamp lights up.
Why it works
The rule goes further: any small piece that closes up before it reaches the pump is wrong. The lesson about islands takes that idea to bigger pieces.