Mancala World


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Inventor: Clark Daniel
Rodeffer, 2000
Ranks: Eight by Eight
Sowing: Single laps
Region: USA

Inchworm was invented by Clark D. Rodeffer (USA) in November 2000. The game was submitted to the "First Annual 8x8 Game Design Competition" sponsored by About Board Games, the Strategy Gaming Society and Abstract Games Magazine, 2000.

Inchworm is a two-person game, which combines a mancala-like move mechanism with the piece capturing aspect of Go. Pieces may move individually or as groups by stacking and unstacking them, mimicking the motion of an inchworm.

After Inchworm had been implemented on Super Duper Games on August 28, 2008, it was soon discovered that the game needs major rules modifications, otherwise it is easy to break.



Inchworm Board

Inchworm is played on a standard 8x8 chess board with two sets of 25 stackable playing pieces in contrasting colors (red and blue poker chips are recommended). Players also need some means of keeping score. Paper & pencil can be used, but a cribbage board is also convenient.

At the start of the game the board is empty. Each of the two players (called Red and Blue) have a stock of 25 pieces off-board.

Original Rules

During his own turn, a player may do exactly one of the following five things (passing is not allowed unless both players agree that there is no legal move):

  • If his stock is not empty, he may drop exactly one of his own pieces onto any vacant square.
  • If his stock is not empty, he may drop exactly one of his own pieces on top of any of his own pieces already on the board, thus forming or increasing a stack. Using drop moves, a player may increase a stack to any height, until his stock is empty.
  • Collect a linearly connected group of his own pieces or stacks into a single combined stack. Pieces or stacks so collected may lie along any straight line or diagonal.

An Inchworm

  • Distribute one of his own stacks into a winding group of individual pieces beginning with the space where the stack started. In distributing stacked pieces, any path may be taken, including straight lines and diagonals, but the entire stack must be distributed into individual pieces. If any pieces of either color were surrounded, these are taken simultaneously as prisoners and one point is immediately scored for each.
  • Rescue all prisoners held by his opponent by returning them to his stock.
Any individual pieces and/or stacks of pieces that are orthogonally surrounded, including those trapped against one or more edges of the board, by opposing pieces or stacks of pieces may be taken as prisoners and scored, no matter how those pieces came to be surrounded. Playing so that your own pieces are captured is perfectly fine, and may even be a useful tactic if the stock is empty or nearly so, or if opposing pieces are simultaneously captured by such a move.

The first player to score at least 60 points wins. For shorter games the score can be reduced.


Clark D. Rodeffer suggested several variants in the paper he originally submitted.

1. Board:
A variation that makes capturing more difficult (and hence lengthens the game) is to eliminate the side and/or baseline board edges, wrapping them around like a cylinder or torus, respectively. Capturing on a cylindrical board is more difficult than on one with edges to the side, and capturing on a board shaped like a torus is even more difficult.

2. Capture Rule:
Another variation that increases offensive potential is to allow placement of captured opposing pieces. Their usefulness in filling eyes in your opponent's formations can increase game tension and result in faster scoring. However, this can lead to a trivial situation where opposing pieces are repeatedly played into the eyes of your own formations and recaptured and scored over and over again, reducing the game to a race.

3. Handicap:
If one player is noticably stronger than the other, a fair handicap system is for the stronger player to use fewer pieces. As the stock empties, the stronger player will need to spend more turns rescuing his prisoners, thereby giving the weaker player a few extra turns to gain positional advantages. One or two pieces constitute a relatively minor handicap, but five pieces is significant.

Drawing Strategy

The original rules could lead to a degenerate game since it was possible to form an impenetrable wall of orthogonally connected stacks dividing the board into two areas and/or a group with two "eyes" (i.e. squares surrounded by pieces of one color and thus unreachable by the opponent).

Revised 'Modern' Rules

Several ways to fix the game were discussed on Super Duper Games:

  • Forbid the formation of groups with more than one eye.
  • Forbid a single orthogonally connected group to touch more than one board edge.
  • Allow any group to be surrounded and captured, even if it has internal eyes, but ...
  • award points for surrounded open spaces to the defender and/or
  • only the smaller group (in terms of either total area or number of pieces) is captured and/or
  • re-introduce the possibility of ko by giving life priority to the acting player.
  • End the game at the current score if no capture is made in X number of moves where ...
  • X is a fixed value or
  • X is some yet-to-be-determined function of the numbers of pieces on the board.

Eventually the following rules (suggested by Laurie Menke) were agreed upon:

  • At the end of each turn players look for groups with no "liberties" (orthogonally adjacent empty squares).
  • For a given group X all the surrounding groups are analyzed.
  • If any one of those surrounding groups has no liberties, then the capture takes place as usual.
  • If, however, all the surrounding groups have at least one liberty, then the group X is safe.

External Links


© Ralf Gering & Clark D. Rodeffer
Under the CC by-sa 2.5 license.

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