Go

Go is a territory game in which two players take turns placing black and white stones on the points where the lines of the board cross. The rules fit in a few sentences; mastering the game takes years. On CetinsGame you can play Go on a 9×9 board under Chinese rules (area scoring), against the computer at three levels or with a friend on the same screen. Your Brain points go to Go's own leaderboard. The Mind games collection on the site has other mind games too, such as Reversi, Hex, Dots and Boxes, Tower of Hanoi, chess, Dama and Mangala.

To own more area than your opponent when the game ends. Your area is your living stones on the board plus the empty points surrounded only by your stones. Capturing is not a goal in itself; captured stones matter because they shrink your opponent's area and grow yours. Black moves first, so White receives 7.5 points of komi; thanks to the half point, Go never ends in a draw.

Placing a stone: on your turn, tap an empty intersection. Your stone goes there and never moves again; a small ring marks the last stone played.

Capturing: the empty points next to a stone, or next to a group of stones connected along the lines, are its liberties. Fill the last liberty of an opposing group and all its stones leave the board. A group with only one liberty left is in atari.

Forbidden points: you can't play where your stone would have no liberties (suicide), unless that move captures opposing stones. A move that returns the board to a position seen before is also forbidden (ko). If you tap a forbidden point, no stone is placed and the game tells you why.

Passing and the end: when there is nothing valuable left to play, press Pass. When both players pass in a row, the game ends and the count begins.

When the game ends, the computer suggests which groups are dead: stones stranded inside the opponent's area with no chance of escape are shown faded, areas are marked with small squares and the live count appears at the top of the screen. If you disagree, tap a group to switch it between dead and alive, then press Accept the count. Against the computer, if your marking differs from the computer's, it does not accept the count and the game goes on: under area scoring, playing inside your own area costs no points, so you settle the disputed stones by playing. You can also press Keep playing to leave the count and return to the game yourself. In a two-player game you mark the dead groups together and accept once you both agree.

• Learn: a 6-step tutorial teaches the rules with small positions on a 7×7 board: liberties and capturing, capturing a group, suicide, ko, two eyes and counting. In the first four steps you make the move yourself; the last two are shown on the board.
• Against the computer: Easy thinks very briefly and suits first games. Medium decides by playing thousands of trial games. Hard is the strongest level, yet it cannot beat a strong club player. Medium and Hard may resign when they see the game is lost. You choose who makes the first move: You, Computer or Take turns; whoever starts plays Black.
• Two players: take turns on the same screen; there are no interstitial ads in this mode or in Learn.

Beating the computer earns 15, 35 or 70 Brain points depending on the level; a loss never takes points away. After a lost game you can start a rematch: win it and the points are doubled. What would a master play? shows on the board the move the Hard level would choose right now; you have 3 per game, the first is free and the rest are unlocked with a rewarded ad. Sometimes the master suggests passing. Undo takes back your last move and the computer's reply; it is unlimited, but a game where it was used gives no points. Resign in the pause menu ends the game. Your points go only to Go's own leaderboard. The Badges button on the game screen shows eight badges: Learned, Easy, Medium, Hard, Three in a row, Master hunter, With a friend and Wide territory. The statistics keep your wins by level, your longest winning streak and your biggest point margin.

On a 9×9 board every stone counts. Early on, corners and edges are the easiest places to make territory, because the edge of the board works as a ready-made wall. On a small board stones near the centre are strong too: a centre stone influences all four directions and helps split your opponent's groups.

Keep your groups connected; a cut-off, weak group becomes your opponent's target. Every group wants two eyes: a group with two separate empty points inside can never be captured. Before trying to rescue a stone in atari, check whether it can really escape; adding stones to a stone that can't be saved only makes the loss bigger. Pass once the borders are settled, but don't pass early while you are behind.