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: Thus a serieshelpmate in "n" moves consists of "n" legal unique moves by Black (all but possibly the last non-checking moves) followed by one move by White that mates Black. To the right is a serieshelpmate in seventeen by  Thomas Rayner Dawson (published in "Fairy Chess Review", 1947). 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. (As usual, chess problems with unintended multiple solutions are considered flawed; they are often said to be "cooked".) The solution here is: