Two first-prize problems by Geoff Foster and Ian Shanahan

Congratulations to Geoff Foster and Ian Shanahan whose works have gained First Prizes in the respective tourneys of two major problem publications, feenschach and StrateGems. Both problems are series-helpstalemates, a type of series-mover in which Black plays a number of consecutive moves to reach a position where White can deliver stalemate. The two compositions also share a theme: multiple self-unpins by the black pieces, impressively rendered in each case.

Let’s analyse the first, joint work. Black has six units besides the king that must be immobilised. Four of them can be pinned by the available white pieces, one can be captured by White’s stalemating move, and if that move is Sxh3, the knight will block the remaining black unit, the h4-pawn. Such a knight move will also cover the f4-flight. This plan requires Black to promote the b-pawn and rearrange the pinned pieces – the aim is to obstruct the flights on d4 and d5, and to relocate the f5-rook which is pinning the white knight. 1.b4 2.Sxb2 3.Sc4 4.b3 5.b2 6.b1=S 7.Sc3 8.Sd5 9.Re6 10.Sc6 11.Sde7 12.Rg6 13.Rd5 14.Sd4 15.Se5 16.Sf5 17.Rg3 18.Rh3 Sxh3. The black pieces unpin one another by interposition eleven times (the underlined moves), a record number when this problem was published.

Geoff’s solo effort extends the number of unpins to fourteen, which is the current record. In this position, not counting the black king and the blocked f6-pawn, Black needs to disable six units. Again, four of them may be pinned by the white line-pieces, and one captured by the stalemating move. The only way to deal with the last black unit is to pin it with a promoted piece, i.e. Black will place a piece on e7 in anticipation of White’s final move, fxe8=Q. Note also that Black’s white-squared bishop cannot be fully restrained by a diagonal pin; nor can it be pinned while blocking the king’s orthogonal flight-squares, which are black. Therefore the only role left for this bishop is to be the captive on e8. 1.Rd6 2.b5 3.b4 4.b3 5.Sb6 6.Rd5 7.b2 8.bxa1=B 9.Be5 10.Sg4 11.Be4 12.Bd6 13.Sc4 14.Rf5 15.Sge5 16.Bc6 17.Be7 18.Rd5 19.Sd6 20.Bxe8 fxe8=Q. Another attractive sequence where the precise move order is determined by intricate pinning/unpinning effects.