Yugo

Overview

Yugo thumbnail imageYugo is a finite Go variant for two players (Black and White) where permanent pieces of the player's color are used for capturing. It was designed by Luis Bolaños Mures in 2017, inspired by Mark Steere's Redstone.

Objective

The objective of Yugo is to have a higher score than your opponent at the end of the game. Your score depends on the amount of territory that you have surrounded and the number of pieces that you have on the board.

Material

The board is a square grid made of an equal number of horizontal and vertical lines. Pieces are placed on their intersections, also called points. The suggested board sizes are between 9 and 19 points per side.

19x19 board

There are two kinds of pieces: pawns and kings. There is also a special token called button.

From left to right: black pawn, black king, white pawn, white king.

Definitions

A player's group is a set of orthogonally contiguous pieces of that player's color. Pawns and kings can be part of the same group. A group is as big as it can be, i.e. it's never a subset of a bigger group.

liberty is an empty point orthogonally adjacent to a group. A group without liberties is said to be surrounded.

A player's territory is a set of orthogonally adjacent empty points such that all points orthogonally adjacent to it are occupied by pieces of that player's color.

One white group and two black groups    Territories

In the first picture, there is one white group and two black groups. The marked points are all the liberties of those groups.

In the second picture, the set of 6 empty points in the top left corner is a white territory and the set of 4 empty points on the right side is a black territory. The set of 7 empty points in the bottom left corner is not a territory of either color because it's adjacent to pieces of both colors.

Play

The game begins with an empty board. The button is placed next to it. Black plays first, then turns alternate.

On their turn, a player must perform exactly one of the following actions:

  • Take the button, provided that none of the players has taken it before.
  • Pass, provided that the button is already taken.
  • Place a pawn of their color on an empty point such that the number of surrounded groups remains unchanged.
  • Place a king of their color on an empty point such that the number of surrounded enemy groups is increased, and then remove all pawns from all such groups. Lastly, in the resulting position, remove all pawns from all surrounded friendly groups.

    

On the left, White can't place a pawn on the marked point because the number of surrounded groups is increased. They can't place a king there, either, because the number of surrounded enemy groups is not increased. Black, however, can place a king on that point and remove all pawns from the newly surrounded white group, as shown on the right.

    

On the left, White can place a king on the marked point, which increases the number of surrounded groups of both colors. The surrounded black group is checked for removals first, but none are possible, as it contains no pawns. Next, since the white group remains surrounded, the pawn that it contains is removed, as shown on the right.

Komi, button and handicap

The komi is the whole number of points which is added to White's score at the end of the game as a compensation for playing second. The value of komi is agreed upon by both players before starting the game. A komi of 7 should be roughly adequate on 9x9 and bigger boards.

The button a special token which is used to avoid ties. At the end of the game, the player who has taken the button gets an extra half point in their score.

If there is a large difference in skill between the players, a handicap can be used to compensate for it: the weaker player plays with the black pieces and is allowed to place several pawns before their opponent makes their first move. The number of handicap pawns is agreed upon by both players before starting the game. The commonly used values lie between 2 and 9.

End of the game
Play stops when both players pass consecutively.

At this point, the players may agree which groups, if any, can be removed from the board without changing the scores that would result from continuing the game. If there is such an agreement, the agreed groups are removed, the game ends and the resulting position is used for scoring. If the players don't agree which groups should be removed, play is resumed. In this case, when both players pass consecutively again, the game ends and the current position, without further removals, is used for scoring.

A player's score is the number of empty points in territories of their color, plus the number of pieces of their color in groups with one or more liberties, plus the number of enemy kings in groups without liberties, plus half a point if they have taken the button, plus the value of komi in the case of White.

Finally, in handicap games, a number of points one less than the number of handicap pawns is subtracted from Black's score.

The player with the higher score wins the game.


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