Spoiler alert: the following provides the answer to yotta's puzzle. Read at your own peril!
Whenever I see a puzzle, all my insecurities come to the surface. What if I can't do it? What if this is too tough for me? Then I have to discipline myself to look at the problem with my whole mind using all the theory I have learnt.
In the present instance my thinking process went like this:
1) Black has only one move. That move is by a Pawn and after that it is stalemate if we don't allow some move. Good news: any check we make is potentially checkmate.
2) Therefore I cannot Queen the Pawn to checkmate in the time allocated.
3) I must cover the e4 square with some piece, other wise it will not be checkmate.
4) The only piece that can do that is the Rook.
5) Moving the Rook to say a2 and then a4 to give mate will release the King to escape from the net.
6) If only (key thought here) I could move the Rook to d4... Drat, the King and the Pawn are covering d4.
7) Hmmm maybe if the King moved away I could put the Rook on d4 with a double check of some sort. That is crazy! There is no way you can do that. Wait, maybe it is not so crazy. How can we engineer a double check? The Bishop is in completely the wrong place. Maybe if the Bishop were somewhere else.
8) Let's try moving the Bishop to c1. Black can only play e6. OK, now Black is in danger of stalemate. How can we get that double check going?
9) There really is only one possibility: put the Rook on d2, so that the Black King can move once again. Now he has only one square to move to: f4. This is looking a little discouraging, because the King is attacking the Pawn on g4, and it is is unprotected. Not only that, the King can go back to e4 as well. And the Pawn on e5 is watching d4. and that Pawn can move to e4. Maybe we can get our idea to work after all.
10) We now unleash the double check: Rd4 is checkmate. Black cannot take the Rook on d4 because of the check from the Bishop. He cannot move to e4 because the Rook is covering that square. and he cannot take the Pawn on g4 because the Rook is protecting there too.
A good problem has some lesson that it teaches. In this instance I see several lessons, I'm sure there are more:
- Be careful when your opponent is in a bad position: stalemate punishes the slightest drop in vigilance. There are a sad number of instances on the ChessConquest site to show that is not just a mere theoretical possibility.
- When your opponent has no legal moves with his king look carefully: any check could then literally be checkmate.
- A double check (check from two pieces at the same time) is a tremendously powerful weapon. When King is in double check, there is no time to take one of the pieces because the other piece is still giving check. One cannot put another piece in the way because the attacks are coming from two directions. The king can only swallow his dignity and flee as fast as he can.
- be creative in games. Don't be scared to say "if only" if that triggers the thought, "but how can we make it happen?"
If you did not solve a puzzle, ask yourself what piece of theory did you either not know, or that you did not apply. If this is a new area for you, make a point of studying that theory using a book or a web resource. If you should know it, see if you can find further examples on the Web to sharpen your skills.