Ko & suicide
Two rules in Go exist to stop the game collapsing into loops and impossible positions. They are the rules beginners trip over most often.
Ko: no instant retaking
If you capture exactly one stone with a stone that has only one liberty, your opponent may not immediately take it back — otherwise the two of you would bounce the same stone forever.
The ko shape
Black captures one white stone. White must play elsewhere first, then may retake the ko.
There is no ban on a ko fight: both sides can keep playing around the ko, and the surrounding points decide who takes it. Our engine applies the same simple-ko rule you see here.
Suicide: you may not fill your own last liberty
You cannot place a stone that leaves one of your own groups with zero liberties — unless that move captures an enemy group first and creates liberties that way.
- So a lone stone surrounded on all four sides is an illegal move, not a way to remove your own stone.
- The exception matters: if filling your own last liberty captures an adjacent enemy stone, the move is legal — the capture gives your group room.