(1) Slobodan Mladenovic
4.hm Probleemblad 1987, 06.09.2011

If it were Black to move, then White would be able to mate at once. For example, 1...f3 allows 2 g4#, if the bishop moves then 2 RE5#, while a move by one of the pieces surrounding the white queen would allow the queen to mate at b1, e4 or h7. So Black is already inz ugzwang and White only needs amwaiting move to solve the proble. However, that would be too simple (it is a world championship, after all). A quick checks shows thatere is no viable waiting move, for example 1 Bg7? or 1 RE7? blocks the queen's path to h7. The solution involves disrupting, at least to some extent, the pre-existing mates. I found the lkey by noting that three of the mates (Qb1, Re5 and Qh7) cover the e4-square, and so it might be possible to release White's guard on this square and still preserve at least some of the mates. This suggests a movce by the c3-knight and noticing that ...Ke4 could then be met b7y 2 Bg6# only reinforced the feeling that this is the correct path. Where should the knight move? One problem is that after 1...f3, the reply 2 g4 is no longer mate, so there has to be a substitute mate in this line. A natural idea is to replace the pawn mate by 2 Ng3#, but for this to work White's first move must cover f4. This immediately leads to the key 1 Nd5!, which also substitures 1...Rd6 2 Ne7~ for the earlier mate by Qe4. The other mates stay the same.

[1.Nd5 Ke4 (1...Nbxd5 2.Qb1# ; 1...Ncxd5 2.Qh7# ; 1...Bf7 2.Re5# ; 1...f3 2.Ng3# ) 2.Bg6# ] *