The chess problems I have chosen for this post are logical. That term refers to the way in which the solution is structured. In the initial position, White has a so-called main plan, a series of moves with which he wants to checkmate. At first, the execution of this plan fails to a refutation that Black has up his sleeve. Therefore, White first executes a foreplan, whereby Black's defence to the main plan is negated in some way. Roughly speaking, that's what logical problems are about.
Let's start with a lightweight example.
|The main plan is to play the queen to the b-file and give checkmate on b8. But the attempt 1. Qb1? Bg3! is premature. Another idea that fails is 1. Qg2+? d5!. |
1. Qg7! (2. Qxd7 3. Qc6/Nb6#) Be7 2. Qb2 Bd6 3. Qg2#
The bishop was lured away to another diagonal and thus was forced to replace the good defence Bg3 with the bad defence Bd6. This caused the interference with the pawn d7. This theme is called Interference Roman (translation found here).
Wow! True, an experienced solver might consider this move even without exactly knowing how to proceed thereafter — it's the feel. Otherwise, deep thinking is required.
White now threatens 2. Rh7! 3. Rxh2 4. Ng2#. The point of going to a8 is to avoid 2. Rxh7 being check. In doing so the king has to avoid b8 because of the potential pin by the black bishop coming to h2. Why 1. Kc8? is wrong will be explained later.
1. - Rh8+
Black is so tied down that this is the only way to challenge White's idea. White continues with another incredible move:
2. Rxe8+ 3. Ka7!
Not 3. Kb7? Rb8+ 4. Kxb8 Bh2! This also makes clear that in case of 1. Kc8? the white king would not have been able to escape the h2-b8 diagonal in time.
Black can now no longer guard g2, so that after
3. - Ra8+ 4. Kxa8
there is no way to prevent 5. Ng2# or (when Nf2 moves away) 5. Nd3#.
Alternatively, the rook can only return.
2. - Rh2
By now, we have achieved our goal, so that the main plan can be executed.
3. Re7 ~ 4. Rxe2+ Bxe2 5. Qe2#
|This one is probably easier to solve despite its length.|
White's main plan is Rf8 followed by Rc8#, but Black is stalemated. The foreplan is to build a bishop-rook battery on g1,f2 with the black king on c5 and play Rf8+. But this requires the protection of the pawn d6, so that playing the pawn e2 to e5 is another foreplan. Important things to observe: White always has to a) protect d6 and b) give a check when the king is on c5. See and enjoy how all this is accomplished.
1. Bc1 Kc5 2. Be3+ Kc6 3. Bf4 Kc5 4. Rf5+ Kc6 5. Be5 Kc5 6. Bh2+ Kc6 7. Rf6 Kc5 8. Bg1+ Kc6 9. e3 Kc5 10. e4+ Kc6 11. Bh2 Kc5 12. Rf5+ Kc6 13. e5 Kc5 14. Bg1+ Kc6 l5. Rf2! Kc5 16. Rf8+ Kc6 17. Rc8#
We see a variety of self-interferences employed by White to relieve the stalemate. A very nice puzzle.
|Black to move allowed White to mate on d4 or d5. But there is no waiting move. The goal of the foreplan is to lose a move.|
1. Ne8! (threat 2. Nf6 3. Ng4#) Ng8 2. N6c7! Nfe7 3. Ng7!
White now threatens 4. Nxd5+ and 5. Nf5# or vice versa.
3. - Nf6 4. Nce6! and 5. Nxd4# or 5. N(x)f5#.
3. - Nxh6 4. Nge6 Nhf5 5. h6!
There is the waiting move! The diagram position, without the pawn h5, has been repeated. It is Black to move and mate follows on the next move.
Did you notice? During the solution, the two white knights have
swapped places. Moreover, the black knights also performed such a Platzwechsel!