Series-movers

Series-movers are a major category of problems that belongs to the realm of fairy chess, or the unorthodox field that involves changes to the standard rules of chess. The basic convention that White and Black move alternately is dispensed with in series-movers; instead, one player makes a sequence of consecutive moves while the other side remains stationary. The aim of the move sequence varies, which gives rise to three types of problem stipulations: series-mate, series-helpmate, and series-selfmate. In all cases, the player who executes the series must never move into check; it’s also forbidden to give check, except on the last move. For a series-mover to be sound, the sequence of moves in the solution must be precisely forced.

White plays the sequence in a series-mate problem, and the goal is to mate Black in the specified number of moves. So Black does not move at all in this sub-genre. In 151, a plausible plan for White is to promote one pawn to a queen for Qxg7 mate, while using a second promoted piece to guard g7 and to shield the black king from check when the queening occurs. But this will not solve in time, e.g. 1.d4 2.d5 3.d6 4.d7 5.d8=B 6.Kb1 7.b4 8.b5 9.b6 10.b7 11.b8=Q 12.Qb7 13.Bf6 14.Qxg7 – one move over the limit. The solution instead requires White to promote to a pair of the least powerful pieces: 1.d4 2.b4 3.b5 4.b6 5.b7 6.b8=S 7.Sd7 8.Sf6 9.d5 10.d6 11.d7 12.d8=S 13.Sf7. The two white units unpin each other in turn and this helps to bring about the unique move order.

The most common form of series-movers is the series-helpmate. In this type, Black makes the sequence of moves and aims for a position where White can mate in one. Solving a series-helpmate usually begins by finding a suitable mating square for the black king. Here the king can’t be mated on a8, since a mating move like Ra6 would require b7 to be blocked by the knight but the other flight on b8 is unreachable by the light-squared bishop. A similar final configuration with the king placed on h8 does work, however, because the bishop can be pinned on g8. To transfer the king from one corner to another, Black must use the other pieces to shield it from the rooks’ checks on multiple lines. 1.Kb7 2.Sd6 3.Kc6 4.Kd5 5.Ke5 6.Se4 7.Sf6 8.Ke6 9.Kf7 10.Sh5 11.Sg7 12.Kg8 13.Kh7 14.Bf7 15.Bg8 16.Kh8 for Rh6.

In the initial position of 153, Black’s pieces seem already well-placed for confining the king on b1, and if not for the obstructing pawn on f3, White’s h1-bishop would be able to deliver mate straightaway. Hence Black proceeds to get rid of this pawn, a task that requires the rook, since a bishop would check on f3. 1.Bxh8 2.Bb2 3.Bc1 – these starting moves are designed to clear b2 for the king, without giving a rook check on the rank – 4.Kb2 5.Bb1 6.Ra3 7.Rxb3 8.Rxf3. Now Black shuffles all four pieces back to their original places, 9.Ra3 10.Ra1 11.Ba2 12.Kb1 13.Bb2 for Be4.

In a series-selfmate, White plays the consecutive moves to reach a position where Black is forced to inflict mate. Since checking on the last move of a sequence is allowed, White will often give such a final check, to restrict Black’s legal play to the mating move(s), though (as in normal selfmates) it is also possible to compel the mate by means of zugzwang. White uses the former method in 154. Here the arrangement of the two kings and the black knight suggests that White will check on c7 with a promoted knight to force …Sxc7 mate. This plan necessitates self-blocks on a5 and b6, as well as control of b8 to constrain the black king. 1.d8=B 2.e8=R 3.Re6 4.Ba5 5.Rb6 6.e6 7.e7 8.e8=S 9.Sc7+ for Sxc7. White promotes to three different types of pieces, an idea shown with perfect economy here.

The three main forms of series-movers all finish with a targeted mate, but we can envisage for each a corresponding type where stalemate is the goal. Thus the series-helpstalemate stipulation means that Black plays the sequence of moves and seeks a position where White can give an immediate stalemate. In 155, Black has three major pieces that are mobile on the second rank, but the pawn structure on the king-side seems ideal for incarcerating them, so 1.Qh2 2.Qh4 3.Rh2 4.Rh3 5.Rah2 6.g2 7.g3 8.g4 9.g5 for Bxd3 stalemate looks tempting. However, this unique sequence is only a try, because 6.g2 is a prohibited check! Another try, to lock in the queen on h2, is 1.Qc7 2.Rh2 3.Rh4 4.Rah2 5.R2h3 6.g2 7.Qh2 8.g3 9.g4 10.g5 for Bxd3, but this exceeds nine moves. The solution has the queen heading for h3: 1.Qc8 2.Rh2 3.Rh4 4.Rah2 5.g2 6.g3 7.Qh3 8.g4 9.g5 for Bxd3.