[[quote]] A proof game is a type of [[retrograde analysis]][[chess problem]]. The [[solver]] must construct a game starting from the initial [[chess]] position, which ends with a given position (thus proving that that position is reachable) after a specified number of moves.
When published, shortest proof games will normally present the solver with a diagram - which is the final position to be reached - and a caption such as "SPG in 9.0". "SPG" here is short for "shortest proof game" and the "9.0" indicates how many moves must be played to reach the position; 9.0 means the position is reached after black’s ninth move, 7.5 would mean the position is reached after seven and a half moves (that is, after white’s eighth move) and so on. Sometimes the caption may be more verbose, for example "Position after white’s seventh move. How did the game go?".