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376. Arthur Mosely
Good Companions 1916
Mate in 2

Set mates are provided for all possible black moves: 1…R~ 2.Sd2, 1…Rxd3 2.Qe6, 1…Sb~ 2.Sc5, and 1…Se~ 2.Bxf5. White has no way of retaining all of the set play, e.g. 1.Kb8? Sc6+!, 1.Be6? Rxd3!, while 1.Rc3? (threatening 2.Qe6) fails to 1…Rxd4! The key 1.Qa3! (waiting) grants a flight on d3 but sets up a battery to answer 1…Kxd3 with 2.Sd2. The mate following the correction move 1…Rxd3 is changed to 2.Qxe7. The remaining play is unchanged: 1…R~ 2.Sd2, 1…Sb~ 2.Sc5, and 1…Se~ 2.Bxf5.

Andy Sag: Complete block with one post-key mate change and one added pure mate after flight capture. A try worth mentioning is 1.Kxb7? (2.Sc5) Rb1!, pinning the knight.
George Meldrum: A wonderful key move and after the black king captures the rook, White needs to cover five squares to provide a mating net.
Jacob Hoover: After the key, 1…R~ still allows 2 Sd2 but this time it's an indirect battery play, and the response to the correction 1…Rxd3 (still a self-block) changes to 2.Qxe7. White also has an answer for the flight that the key grants: 1…Kxd3 2 Sd2 (distinct from earlier due to being a direct battery play as opposed to indirect). A rather nice mutate with black correction in both the virtual and actual play.
Ian Shanahan: Fantastic flight-giving zugzwang key. I found this to be most difficult to solve. A concurrent changed-mate after 1…Rxd3. This problem is masterful – just as one would expect from Mosely.

 
377. George Sphicas
The Problemist 1989
Series-helpmate in 7

The black king could potentially be mated on many squares, but the shortest sequence involves placing it on e2 for a queen mate on c2. This scheme requires Black to promote various pawns to self-block on f1, e1, and f3. Further, since Black is initially in check, the first move has to be a promotion on c1, and the new piece must not interfere with the eventual mate. 1.c1(S) 2.f1(B) 3.e1(R) 4.Ke2 5.d1(Q) 6.Qd5 7.Qf3 Qc2 mate. When first published, this seven-move problem held the economy of length record for a series-helpmate showing the Allumwandlung theme. But subsequently the record of six moves has been achieved, which is the theoretical minimum (given that Black must make four promotion moves plus two queen moves – one diagonal and one orthogonal – to ensure that the queen couldn’t be replaced by another promoted piece). Thanks to Michael McDowell for pointing out the correct source of this problem.

Jacob Hoover: All of the possible promotions (knight, bishop, rook, queen) are seen here, so it's an Allumwandlung.
Andy Sag: A tough one to solve as there are 14 feasible squares for the queen to finish on and c2 was the 8th one I tried. I guess you call it an Allumwandlung as it uses all possible promotions.
Ian Shanahan: Seeing the name above the diagram, one expected the four promotions (AUW, here capture-free). The only blemish is the black king being initially in check, a necessary “trick” to force accurate move-order.