Copyright (c) 2003 Bill Taylor
Gem is actually two twin games (Gem-Y and Gem-EE) played on the following 5-side board.
- TURN - On each turn, each player drop one friendly stone in an empty cell.
- Gem-Y game: a chain of adjacent stones touching 4 sides, or any side and its opposite 2 sides.
- Gem-EE game: a chain of adjacent stones touching 4 sides, or 2 groups touching 3 sides each.
An Gem-Y example
Black just dropped the marked stone threatening to connect two edges at the corner (thru the green dots). White can try to prevent it by playing at . If Black drops at  then .