The pawn cross theme

A pawn placed on its initial rank has four potential moves – two forward steps and two captures, the maximum possible for the unit. When such a pawn makes all four of these moves in a problem’s solution, the resulting theme is traditionally called Albino or Pickaninny, depending on the colour of the pawn. The second term carries racist connotations, unfortunately, and it’s a contentious issue among problemists as to whether it should be replaced in contemporary chess writing. On this site, I have opted for WP4 and BP4, even if they seem a little dry. However, a recent issue of The Problemist Supplement employs another alternative that may be preferable; a solver’s comment there from Brendan O’Malley refers to a pawn cross. This colour-neutral term, describing the geometric pattern formed by the pawn’s moves (similar to the established king cross and bishop star) seems straightforward and appropriate. So henceforth that theme name will be adopted here.

Although this two-mover wasn’t the first to combine black and white pawn crosses in a single problem, it’s a particularly clean example. The key 1.Qa8! threatens the battery mate 2.cxd7. All four moves by Black’s d7-pawn eliminate the threat and they provoke different responses, as required by the theme: 1…d6 2.Sxg7, 1…d5 2.Sg5, 1…dxe6 2.c7, and 1…dxc6 2.Qxc6. White’s c2-pawn executes four different mates, all induced by the same black rook (a bonus unifying effect): 1…Ra3 2.c3, 1…Rb3 2.cxb3, 1…Rd3+ 2.cxd3, and 1…Rg5 2.c4. Curiously, there is no subsidiary play at all besides the eight thematic variations, as the threat is not stopped by any other black move.

Black’s only mobile units are the king, with flights to g6/g5, and the pawn on g7. White has mating responses already prepared against all four pawn moves, which variously deprive the king of its escape squares: 1…g6 2.Qd5, 1…g5 2.Qh7, 1…gxh6 2.Qg4, and 1…gxf6 2.Sd6. Thus a black pawn cross is obtained in the set play. White must deal with the king moves as well, and the try 1.Qf7? (threatening 2.Rc5) does so but is spoiled by 1…gxf6! Instead, 1.Qe8! puts Black in zugzwang, while it also removes the g6-flight and provides for 1…Kg5 with 2.Qh5. Surprisingly, White has abandoned the four set replies to the pawn moves, and replaced them all with new mates: 1…g6 2.Qe5, 1…g5 2.Qe4, 1…gxh6 2.Qh5, and 1…gxf6 2.Rc5. A complete change of mates for the black pawn cross is brought about – a sophisticated elaboration on the theme.

Our next problem gives the theme a modern treatment by incorporating significant white tries plus some abstract move patterns. The white pawn’s four options are potential starting moves, three of which are try-moves subtly defeated by Black. If that pawn were to disappear, allowing the queen to guard flights on d2/c2, that would generate three threats: 2.Rxd3 [A], 2.Se3 [B], and 2.Bxf3 [C]. However, any single-step by the pawn obstructs one of these mates, leaving two threats only, and Black is able to thwart both. Hence 1.exf3? (2.Rxd3 [A], 2.Se3 [B]) Bxc2!; 1.exd3? (2.Se3 [B], 2.Bxf3 [C]) Re1!; and 1.e3? (2.Bxf3 [C], 2.Rxd3 [A]) Se5! – the labelled threats AB-BC-CA form a cyclic pattern. The double-step 1.e4! avoids the obstructions and carries the triple-threat. The threatened mates are then forced one by one when Black plays the moves that previously refuted the tries: 1…Bxc2 2.Bxf3 [C], 1…Re1 2.Rxd3 [A], and 1…Se5 2.Se3 [B]. Such a separation of multiple threats into distinct variation-mates is known as the Fleck theme. It’s also a nice touch how in these three main variations, Black and White employ matching pieces.

Another pawn-related theme that involves four elements is the Allumwandlung, where promotions to queen, rook, bishop, and knight all take place. This three-mover achieves a striking blend of that promotion task and a pawn cross. The key 1.b7! creates two threats, 2.b8=Q (covering both flights on b6/d6) and 2.b8=S+, that are separated by two black pawn defences. 1…g5 compels 2.b8=Q g4 3.Qc7/Rc5 (this dual mate is a minor flaw); not 2.b8=S+? Kb6/Kd6 when the black pawn prevents the bishop from giving mate. Conversely, 1…g6 forces 2.b8=S+ Kb6 3.Be3, 2…Kd6 3.Bf4; not 2.b8=Q? gxf5 3.Qc7+ and the king escapes to d5. The other two black pawn moves deter both promotion threats. After 1…gxf6, 2.b8=Q? stalemates, while 2.b8=S+? allows 2…Kd6 3.Bf4+ Ke7; White must choose 2.b8=B, then 2…Kb6 3.Rxf6 (2.b8=R? Kd6 3.Rb6+ Ke7). And after 1…gxh6, 2.b8=Q? again stalemates, and 2.b8=S+? has no follow-up bishop mates; only 2.b8=R works, then 2…Kd6 3.Rb6 (2.b8=B? Kb6 and 3.Rf6?? is illegal). The by-play consists of 1…Kb6 2.b8=Q+ Ka6 3.Qb7, 2…Kc6 3.Qc7/Rc5 and 1…Kd6 2.b8=Q+ Kc6 3.Qc7/Rc5. A black pawn cross induces a white Allumwandlung; this integration of the two popular pawn themes is rendered in a remarkably light position.