Series-movers

Series-movers are a major category of problems that belongs to the realm of fairy chess, or the unorthodox field that involves some changes to the normal 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, giving 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. Giving check during the sequence is also forbidden, except on the last move.

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 type. In 151, a plausible plan is for White to promote one pawn to a queen for Qxg7 mate, using the 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. Instead, the solution sees White promoting 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 need to unpin each pawn in turn helps bring about the precise order of moves, and such a unique sequence is a requirement for all sound series-movers.

The most prevalent form of series-movers is the series-helpmate, in which Black makes the sequence of moves and aims for a position where White can mate in one. In the initial position of 152, Black’s pieces seem already well-placed for confining the king on b1, and if not for the obstructing pawn on f3, White would have Be4 mate available. Therefore Black proceeds to get rid of this pawn, a task that requires the rook, since a bishop would check upon capturing on f3. 1.Bxh8 2.Bb2 3.Bc1 – these initial 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 options 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 Problem 153. 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 deliver stalemate. In Problem 154, 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. 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, 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.