(4x6) 7B - 6np - 8 - 5k2 - 8 - 8 - 3p1pPp - 5N1K
White retracts and mates in 1.
Solution: Ok, it's a joke! White can't retracts now becose the last move was black. Black and White retracts respectively Ne6xRg7 and Rg4-g7 then White mates with 1 Ne3++