The fundamental paradigm of combinatorial game theory is that games can be added and in fact form a group. If `G' and `H' are games, then `G+H' is a game in which each player on his turn has the option of playing in either move. We say that the game `G+H' is the sum of the local games `G' and `H'.
Each connected eyespace of a dragon affords a local game which yields a local game tree. The score of this local game is the number of eyes it yields. Usually if the players take turns and make optimal moves, the end scores will differ by 0 or 1. In this case, the local game may be represented by a single number, which is an integer or half integer. Thus if `n(O)' is the score if `O' moves first, both players alternate (no passes) and make alternate moves, and similarly `n(X)', the game can be represented by `{n(O)|n(X)}'. Thus {1|1} is an eye, {2|1} is an eye plus a half eye, etc.
The exceptional game {2|0} can occur, though rarely. We call an eyespace yielding this local game a CHIMERA. The dragon is alive if any of the local games ends up with a score of 2 or more, so {2|1} is not different from {3|1}. Thus {3|1} is NOT a chimera.
Here is an example of a chimera:
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