Variations
There are a number of variations on SPGs. The problem may carry a stipulation similar to "Find a game with 8.b7-b8=N mate", which simply means a game must be constructed starting from the initial position and ending on the given move number with the given move. Or it may be a one-sided proof game, in which only white makes moves (this is the SPG analogue to the seriesmover in other types of chess problems). An alternative rule-set may also be specified (such as circe chess or losing chess), or a fairy piece may be substituted for an orthodox piece.
An SPG-type problem is to find the shortest game in which White's and Black's corresponding moves are mirror images of each other. Possible solutions are 1. d4 d5 2. Qd3 Qd6 3. Qh3 Qh6 4. Qxc8#, 1. d4 d5 2. Qd3 Qd6 3. Qf5 Qf4 4. Qxc8#, and 1. c4 c5 2. Qa4 Qa5 3. Qc6 Qc3 4. Qxc8#.
Read more about this topic: Proof Game
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