[Version 2. 2008-07-05. These are not the official rules but a simplifying proposal by Robert Jasiek.]
The game is for the two players Black and White, who use black and white stones, respectively.
The board is a grid of, by default, 19 horizontal and 19 vertical lines forming 361 intersections.
A string consists of a stone and all same-coloured stones connected without interruption via lines.
A liberty of a string is an empty intersection adjacent via a line to at least one of its stones.
A capture is the removal of all opposing strings without liberty.
A play places a player's stone on an empty intersection and then performs any capture.
After a play, a position is the current distribution of black and white stones on the intersections.
A move is either a play or a pass.
The players alternate moves. Black starts on the empty board.
A play without capture may not create a player's string without liberty.
A play may not recreate a position just after any earlier play.
After the first succession of two passes, the players may
either agree on all the stones to be removed, remove them, and then determine the score
or disagree, continue to alternate moves to the second succession of two passes, and then determine the score.
The score is
the number of intersections occupied by black stones
plus the number of empty intersections surrounded only by black stones
minus the number of intersections occupied by white stones
minus the number of empty intersections surrounded only by white stones
minus the komi, which by default is 6.5,
minus 1 if White made the first pass.
The game is
Black's win if the score is greater than zero,
White's win if the score is smaller than zero,
a tie if the score is zero.