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Sim is a 2 player game played on paper starting with 6 dots in a hexagon shape.
Players take it in turn to draw a line between two dots using their own color.
When a player draws a triangle in his color, she loses. Green's turn in this green vs blue game setup and they must give up.
As for this puzzle. it's simpler than it looks because you can only move between the hexagon's outline.
See Also: http://en.wikipedia.org/wiki/Sim_(pencil_game)
link to this puzzle