Chess960: The white pieces are randomly placed on the first row, and the black pieces mirror the white position. The king must be between the rooks, and the bishops must be on different coloured squares. After 'kingside' castling, the king ends up on the g-file and the rook on the f-file, and 'queenside' castling results in the king on the c-file and the rook on the d-file.
Mainplan: -1.Kd6-c5
Q~-(x~)g3+/Rf4-(x~)f2+ -2.c5xb6ep b7-b5 -3.Sb6-a4 & 1.Rxa8#
Refutation: -1…Rf4xPf2! providing for the boxing of wBg1 and thus
placing the original black light-squared bishop on g8, implying that it cannot
be boxed on a8 and hence ruling out -2.c5xb6ep
Solution: -1.Kd4-c5 f6-f5+ -2.Kc5-d4 Rh6-(x~)h5+
-3.f5xg6ep g7-g5 -4.Kd6-c5 Q~-(x~)g3+/Rf4-(x~)f2+ now the dark-squared bB
was initially on h8 and -4…Rf4xPf2 is
illegal because the wR cannot be boxed on h1, -5.c5xb6ep b7-b5 -6.Sb6-a4 & 1.Rxa8#
