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MatPlus.Net Forum Promenade Switcheroos and Cyclotrons

### Switcheroos and Cyclotrons

Very recently, I came across an interesting type of chess puzzles. The goal is to put the black King in checkmate by switching the position of two (or more) pieces. No actual chess moves are made. The pieces simply swap squares.

After solving a few of these puzzles, I must admit that I found them much harder to solve than I expected. Often, the difficulty is a result of having many unnecessary pieces (most of the positions look like they have arisen from regular games). I wonder if this idea can be used to compose interesting retro problems, or more.

For example. try to solve the following puzzle:
J. Coakley 2013
ChessCafe.com
(= 13+12 )
Cycle three pieces so that Black is in checkmate.

One important rule is that the position after the switch must be legal. A position is legal if it could occur in an actual game. This rule implies several things:
a) A pawn cannot be put on the 1st or 8th rank.
b) Both kings cannot be in check.
c) There must be a way to reach the position with a legal white move. Impossible checks, especially double checks, are a frequent "violation".
d) In some cases, retrograde analysis may be required to decide if the position after a switch is legal.

That looks quite interesting -- and it reminds me of a construction tourney by the late Hans Heinrich Schmitz in Andernach 1997:
"Construct a legal position with maximum number of pieces, where the exchange of any two men preserves legality."

Surprisingly this worked with 14+14=28 men!

Dirk Borst, Thomas Brand, Hans-Peter Reich, Ulrich Ring
Andernach 1997
(= 14+14 )

Thanks, Kostas!
The problems seem quite difficult, and very good to attract young minds to a different way of thinking. When you get used to new methods, the initial charm gets lost.