Seriesmover

A seriesmover is a chess problem in which one side makes a series of legal moves without reply at the end of which the other side makes a single move, giving checkmate or yielding stalemate, depending on the precise stipulation. Checks cannot be given except on the last move of the series. There are various types of seriesmover:

Seriesmate: a directmate with White playing a series of moves without reply to checkmate Black.
Serieshelpmate: a helpmate in which Black plays a series of moves without reply after which White plays one move to checkmate Black.
Seriesselfmate: a selfmate in which White plays a series of moves leading to a position in which Black is forced to give mate.
Seriesreflexmate: a reflexmate in which White plays a series of moves leading to a position in which Black can, and therefore must, give mate. Further, White is obliged to mate whenever he can, therefore he has to avoid in his series of moves a position in which he would have mating possibility.

Thus a serieshelpmate in n moves consists of n legal unique moves by Black followed by one move by White that mates Black. To the right is a serieshelpmate in seventeen by Thomas [Rayner Dawson]. An effective way to solve long serieshelpmates such as this is to envisage a position in which Black could be checkmated, and then to work out how such a problem could be reached. Here, with just one knight, the only way to checkmate Black is to have the black king in the corner and another black piece on a2, allowing Nb3 giving mate. It might seem there are many ways to do this, but the need to avoid exposing the white king to check means that there is only one. The piece on a2 has to be a rook, since if it is a queen or bishop, it would cover the b3 square, and if it was a knight, it would check the king. The black king needs to walk half-way over the board to avoid the newborn rook giving check and then back to a1. The solution here is: