I found this lovely helpmate of the eternally delightful Samuel Lloyd, author of so many gems. This is a helpmate from Chess Monthly November 1860, black moves and black and white coordinate their forces to mate black in three moves:
FEN Viewer
The solution is 1...Kf6 2.Ra8 Kg7 3.Lb8 Kh8 4.Le5+ checkmate
Although this leads to 4 moves in the move counter, we are only at 6 halfmoves as expected.
If I had only known this study or known a little more about the mechanics of helpmates, I would not have had such a difficult time with this helpmate:
FEN Viewer
Black moves, and black and white mates black in 3 moves. I got to this from
http://www.praguechess.cz/index.php?...&zobrazeni=ano
checking out about the Chess Train tournament. The study was made by Pal Benkö and has prominent list of non-solvers (people who tried but failed): Bobby Fischer, Vlastimil Hort, Boris Gulko, Rafael Vaganian. Only Anna Myzuchuk solved it when being presented to it in Oldhands vs. Snowdrops 2011 in Marienbad, thus saving a small moral victory against Oldhands as well as being on the winning team. There is even a nice photo below showing all three players pondering on the position on a board with some very strange chess pieces.
I too must admit my defeat against this. After fuming for half an hour with all sorts of mating patterns in the corner I gave up and downloaded software to solve it (shame!). I just had to smack my forehead with "Of course!" when I saw the solution. I think if I had been in the right mindset, for instance using the idea of the Sam Lloyd study, I'm sure I would have found it in a couple of minutes. Please don't try to mate black in the corner!
With the weird checkmates allowed by FIDE even in normal OTB games, I found this "solution": 1...Nc3+ 2.Kc2 (illegal move, legal position) 2...Na2 3.Nb3+ checkmate. Even if you demand the last move (Nb3+), the next last move (Na2) and the position before those to be legal, it would still go "below the radar" and be accepted as a checkmate. Alas, in problem chess all moves need to be legal, which destroys this idea.
Apparently the article doesn't give the solution. Can you solve it here (please, answers in white)?