1.
[
{F:B}{B:24/N7/16/5p2/k1K5 BLACK}
{V:The final seven puzzles explore the wilder fringes of puzzledom. This puzzle is a serieshelpmate in 17, which means that Black plays seventeen consecutive moves, without White moving at all, to reach a position in which White can mate in one. Just as in a normal helpmate, both sides are cooperating. There is one additional rule, none of Black's moves are allowed to give check, except possibly on the last move of the series. Serieshelpmate in 17.;a1a2;Correct;Incorrect.;If a2 were blocked, then White could mate in one by Nb3. The blocking piece must be a rook (if it were a knight, White would be in check and would have no time for the knight mate). Clearly, the f2-pawn must promote to a rook and then move to a2, but at the moment this is not allowed because it would give check.}]

2.
[
The only possible mating position is with a black rook on a2, allowing mate by Nb3. A black knight is no good, because White would be in check and would have no time for Nb3. Black cannot promote his pawn to a rook directly because this would deliver check. So first of all Black must use his king as a shield to block the first rank so that he can promote his pawn, and he must not waste time so he must use the shortest route from a1 to e1.]

3.
[
{S:a1a2}
1...Ka2]

4.
[
{S:a2a3}
2...Ka3]

5.
[
{S:a3b4}
3...Kb4]

6.
[
{S:b4c3}
4...Kc3]

7.
[
{S:c3d3}
5...Kd3]

8.
[
{S:d3e2}
6...Ke2]

9.
[
{S:e2e1}
7...Ke1
Now the pawn can promote.]

10.
[
{F:B}{B:24/N7/16/5p2/2K1k3}
{S:f2f1}{D:100}{X:f1}{P:BRf1}
8...f1R
Black's king must return to a1, but first the rook must move or else ...Ke2 will be check.]

11.
[
{S:f1f2}
9...Rf2
The rook must not move to a2 prematurely, because then the black king's return path will be blocked.]

12.
[
{S:e1e2}
10...Ke2]

13.
[
{S:e2d3}
11...Kd3]

14.
[
{S:d3c3}
12...Kc3]

15.
[
{S:c3b4}
13...Kb4]

16.
[
{S:b4a3}
14...Ka3]

17.
[
{S:a3a2}
15...Ka2]

18.
[
{S:a2a1}
16...Ka1
Everything is in place, and the mating position can be set up.]

19.
[
{S:f2a2}
17...Ra2]

20.
[
{S:a5b3}
18 Nb3 mate.
It is interesting to note how the composer ensured that the order of Black's moves was absolutely unique.]
