(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 
e6x
g7 and g4-g7 then White mates with 1 e3++