A guide to go life and death problems

What a life and death problem is

Life and death is the part of go that asks whether a group of stones survives. Stones that touch along the lines form one group, and the empty points touching that group are its liberties. When a group runs out of liberties it comes off the board. That is a capture.

Every life and death problem grows from that one rule. The attacker takes liberties away, and the defender either makes more liberties or builds eyes. The shape of the question has not changed since the oldest recorded games.

This app takes only the attacking side. Every problem on screen asks the same thing: Black plays first and captures the marked white stones within a set number of moves.

The rules that apply on the board

The board is nine lines each way and stones sit where lines cross. After a stone is placed, any enemy group left with zero liberties comes off the board.

Self capture is not allowed. If your own group would have zero liberties after the move, the move simply does not happen. It is allowed when the same move captures and thereby gains a liberty.

A move that returns the board straight to the shape it had one move earlier is also refused. That is the ko rule in its positional form, and this app does not go as far as ko threats.

All three come from the same code as our sister app Atari Go. A test checks that the two apps answer the same position the same way.

The rules specific to this app

Each problem has a fixed region you may play in. It is the top left corner of the board, and the stones outside it are walls. Neither side may play outside the region.

Black gets one, two, or three moves. Capturing even one of the marked white stones within that budget solves the problem.

White may play anywhere inside the region and may also pass. Passing is usually a loss in a real game, but here giving White one more option makes our claim weaker, and a weaker claim is the honest one. Only then does capture in every variation really mean every variation.

Each problem has exactly one answer. When a problem is generated, every legal black point is played out and the position is kept only if precisely one of them captures. Positions with fewer than five legal points are discarded because there is nothing to choose between.

A wrong move leaves the board exactly as it was. Nothing is taken back because nothing was played. Instead you are told where White answers to survive.

5 legal points

Where to start

Count the liberties of the marked white group first. If there is one liberty left, that point is the answer.

With two or more liberties the question is which one to take first. If filling one of them lets White reach out and gain liberties elsewhere, that is not the move.

Check whether your own stone would suffocate. Points that touch an enemy group often take your own last liberty first.

Going deeper

The answer is often the move that closes White's escape route rather than the one that takes a liberty right away. Taking a liberty is easy to see, but you have to read where White runs afterwards.

In the corner two edges of the board act as walls, so liberties run out faster there than they would with the same shape in the centre.

Sometimes the answer is a throw in, a stone placed inside White's eye space. Even if that stone is captured immediately, White has one liberty fewer while it sits there.

Where people get stuck

If nothing happens when you place a stone, the rules refused the move. It was either self capture or a move straight back into the shape just taken.

If a move looks right but comes back wrong, read White's answer. The screen names the point where White replies. Find it on the board and count again from there.

Once you see the answer, every White reply is listed with the way Black captures against it. Do not read only the first line. Look for the reply that holds out longest.

There are no hints and no undo here. A wrong move changes nothing, so you can try as many points as you like.