Playing Go/2

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The basic rules -- legal plays and how stones die

Life and Death of Stones
Black plays at Q4. White responds at R3. (This is a new move, something the bots have taught us!) Black to Q3. The sequence goes on, with a balance in the end of Black containing White, but White having some territory in the corner.

A second (NW) corner is now played back and forth for a set of moves. In the sequence we find the picture to the left, the White stone at C15 is in atari. This means 'jeopardy'. It is a technical term, however, meaning that the stone has only one avenue of escape, one "liberty". This means, it is in immediate danger of getting captured. If White acts foolishly, that stone would be dead. But she doesn't. And then Black plays at B13, putting another stone in atari.

This is a set exchange, and the moves are well known. There are many possible outcomes, but the most common thing among experienced players is to leave it, with Black hoping to connect his group in atari at some point later.

Official Rules
The rules of Go are simple, but there are some extreme subtleties. These are the simplified rules.
 * 1) The intersection of two lines on the board is a point
 * 2) A path is a sequence of points connected horizontally or vertically
 * 3) A group of stones of the same color are coherent if they lie on a path of the same color
 * 4) A liberty is an unoccupied point next to a group (a solo stone alone on the board has 4 liberties)
 * 5) Groups share liberties
 * 6) A legal play is putting a stone on an unoccupied intersection and removing all enemy stones which have no liberties
 * 7) * one cannot commit "suicide" by placing a piece on the board which would immediately have no liberties.
 * 8) ** the exception is if the nearly-suicidal piece will have liberties by the end of the turn, by removing opponents
 * 9) It is illegal to return the board to a total-configuration which has existed before, during this game.  This is called ko.

Dr. Wildberger plays a few moves in order to set up a situation. White can play in the "suicidal" spot, and win, so it is a legal move. The battle results in a ko battle (back and forth, with provisos about how to repeat). Perhaps Black tires of the back and forth, and ends it, at the cost of getting cut in half in the SW.