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Chess Variants with Inverse Capture

The Season for This Idea?

Recently I was thinking about the Immobilizer in Ultima, which freezes pieces next to it, and I was thinking about other forms of it that might freeze pieces they attack, and then I was thinking about a piece that would freeze whoever attacked it; like the Gorgon, or Medusa.

Then I heard by email that Bill Taylor had just come up with a chess variant reminiscent of Lewis Carroll's _Snark_.

I guess it's the season for inverse capture.

Inverse capture is an interesting rule, and it can be used in many interesting chess variants. You can think of inverse capture as a rule of its own, as a subset of Relay Chess, or as the rule used by the Chameleon in Ultima and other games.

First, let's think about simple Inverse Capture Chess:

simple Inverse Capture Chess

The rules of Fide Chess are used, except that captures are made using the powers of the captured piece.

For example, consider the moves 1.e4, Nf6: the Knight does not attack the Pawn -- instead, the Pawn attacks the Knight!

This is an interesting game to play, and I'm sure it must already exist with some other name; but I think it's especially interesting from a theoretical point of view, because of the question of values:

In this game, is a Queen worth more than a Knight, or less than a Knight? How much?

I also think it's interesting to wonder how the game would work if you had some Inverse Capture pieces on the same board as some normal pieces....

This is an interesting game, in fact a fascinating game, and I highly recommend it; however, I don't want to write too much about it because I want to go on to other topics, and so I'll get you hooked on this game by posing a simple problem -- what is the foolsmate? In other words, from the opening position, assuming both players have the FIDE army and the usual setup, what is the quickest possible checkmate?

You will enjoy this puzzle greatly if you try to solve it yourself before unscrambling the following ROT13-encoded message:

Juvgr nqinaprf gur Xvat'f Cnja naq gur Dhrra'f Ovfubc'f Cnja; Oynpx nqinaprf gur Xvat'f Ebbx'f Cnja gjb fdhnerf naq gura pncgherf gur Dhrra, haqrecebzbgvat gb n Ovfubc!

By the way, according to my interpretation of the rules of FIDE Chess, a Pawn on the first rank can only move forward one square, and a Pawn on the second rank can make an optional double step.

Immediate and Deferred Effects

It is interesting that nobody has drawn the distinction between Immediate and Deferred Effects in chess variant rules.

For example, when Ultima's Immobilizer moves next to a piece, that piece is immediately frozen; however, in FIDE Chess, after 1.e4 d5, the capture 2...d5:e4 is deferred -- it does not happen as a part of the Pawn's move from d7 to d5, but instead the capture must be made as a move by itself, and uses up a move.

Immediate FIDE Capture Chess is clearly not a playable game, but you can see that 1. e4 Nf6 2. e5,e5:f6,f6:e7,e7:d8=Q,Qd8:e8 would at least make it a fast game! (2.Qd1-h5 also captures the King.) The problem is that one capture can lead to another. You could add rules to try to make it playable....

Immediate Capture Rifle Chess is clearly no better unless you add some rules such as check-stops-the-move, or shoot-in-self-defense (as in my old "autorifle Chess").

Immediate Inverse Capture Chess is Bill Taylor's game, which I recommend highly as a good and playable chess variant.

Deferred Conversion Chess, for example, would be a slower and calmer game than Conversion Chess. This is just one example to show how you can find many new variants by applying this new idea of differentiating between Immediate and Deferrred Effects: sometimes the existing game is Immediate, but Deferred would be a better game, sometimes the opposite.

Immobilizers, Basilisks and Gorgons

Immobilizers generate a force field that freezes adjacent pieces. This is an area effect.

Basilisks have a gaze that turns things to stone, while Gorgons turn you to stone if you see them. This is the difference between direct and inverse capture.

In nethack, floating eyes and umber hulks have a gaze attack that only works if you can see them -- nothing happens unless both parties see each other. This doesn't seem useful in chess variants.

Actually, a Gorgon or Basilisk should turn you to stone permanently; this is not at all like the Immobilizer in Ultima.

The point is that normal capture is not the only thing subject to the ideas of deferred, immediate, area, direct, and inverse. Other sorts of piece effect are also susceptible.

For example, the Ultima piece called the "Repellor" pushes all enemy pieces adjacent to its landing square one square away; if a pushed piece has no place to go, it is captured. This is an immediate area effect. With a deferred area effect, it could either move without repelling or repel without moving, but could never do both things on the same move. With an immediate direct effect, it would push the pieces defined by its own "capture power", and with a deferred inverse effect it could stand still and push any Knight that attacked it a Knight's move further away. (There is no "Repellor" in standard Ultima, but Ultima has its own variants.)

If you have followed closely, you have probably already wondered about the next topic.

One, Many, All

An area effect usually affects All the pieces it can. A direct effect usually affects only One piece. If you could affect All, but have the option of leaving some alone, you would affect Many (I can think of no examples of games where Many is used).

With the rules of Deferred Direct All FIDE Capture, after the moves 1.e4 e5 2. Qh5, White threatens to play 3. Q:e5+,Q:f7+,Q:h7 -- a move that puts 3 White Queens on the board at once! Strangely enough, there is a defense:

1. e4 e5 2. Qh5 Qf6 3. Q:e5+,Q:f7+,Q:h7?? Q:e5,Q:f7,Q:f2+

Isn't this a crazy game? But it's a perfectly logical application of "One, Many, All": if a single piece can make more than one capture, it gets to make all of them, and when you make a FIDE capture you occupy the square -- therefore when you make multiple FIDE captures you occupy all the squares at once! (After having spoken of Gorgons and Basilisks, I really ought to mention the Hydra here; but I won't.)

What if a philosopher told us that after "3. Q:e5+,Q:f7+,Q:h7" White does not have three Queens on the board -- instead, it is one Queen that occupies 3 squares!?!? In this case, you would not want to be forced to make All the captures (although it might be an interesting game!), so you might use the rule of Deferred Direct Many FIDE Capture.


By the way, if it is only one Queen occupying 3 squares, how do you move it?


Making multiple FIDE captures leads to the paradoxes of cloning, so let's use Rifle captures for the next few examples...

In Autorifle Chess, the rule was Deferred Direct All AutoRifle Capture, some rules had to be added, and the player got to choose in which order the captures were made. It was playable, it was okay, not a wonderful game; but it was a pretty good accomplishment just to produce a playable game using AutoRifle Capture, where you get to shoot all the pieces you can see in one move, and a Rook, Bishop, or Queen gets to shoot a whole row of pieces at once.

With "Deferred Direct One AutoRifle", Rooks could shoot all the pieces in a row, but the Knights and Pawns and Kings would be no stronger than they are in Rifle Chess. 1. e4 e5 2. Qh5 wins (3.Qh5:f7:e8 is unstoppable).

In "Deferred Inverse One AutoRifle", after 1. e4? e5? 2. Qh5? Black can reply with 2...h7:h5:h2:h1! -- the first capture uses a Queen power, and so the following captures in the same line get to use the same power.

The Power of a Name

After the previous discussion, if I say "Immediate One Conversion Chess", and if you know the rules of Conversion Chess, I have just described a new game to you, with one small change in the rules of Conversion Chess, and with those three words you know all the rules.

We can now create a computer program to spit out the names of umpty-zillion new chess variants, and we will know the rules just by looking at the names of the games.

What we will not know is which few of those umpty-zillion games are good, interesting, playable, okay, or fascinating.

For example, "Deferred Inverse-plus-Direct One FIDE" would be the game I called "simple Inverse Capture Chess" with the additional rule that you could make a normal capture: after 1. e4 Nf6, the Pawn and the Knight attack each other. This is a completely different game, but is it a good one? In order to know the answer, you'd have to think about the game for a few hours, try some openings, look at a few simple endgames, and so on.

The Gorgon as a Chesspiece

Any enemy piece that sees the Gorgon is turned to stone. Any piece that could normally capture the Gorgon can see it.

Stone pieces cannot move or capture, nor can they be captured.

A petrified King is dead, and the game is over (alternative rule: no penalty for a petrified King except that if you are stalemated you lose).


These are the rules we need to make a chesspiece that is like the real Gorgon. Unless we add blindfolds and mirrors to the game, the Gorgon is too powerful to be really interesting, although I think you could enjoy playing a few games where one side's Queen is replaced by a Gorgon Ferz.

Another playable game with a full Gorgon would be to place a neutral and immobile Gorgon somewhere at random on the 4th or 5th rank before starting the game; either side can be petrified by the neutral Gorgon, and the gorgon cannot move.

The HemiDemiSemiGorgon

The Gorgon must be "Inverse", because if it were "Direct" it would be a basilisk. However, we can make it weaker by making it "Deferred" and "One"; of course, that's not a real Gorgon anymore, but what can you do?

If we make every piece a Deferred One Gorgon, the board will soon be full of stone; but if we ADD Deferred One Gorgon power to every piece in addition to its normal power, things get more subtle.

After 1. e4 e5 2. d4?, Black's Pe5 can either stone or capture the Pawn at d4. Capture is much better, because then Black's Pd4 threatens to stone White's Qd1.

1. e4?! a6?! 2. c4!? h5?! 3. Nf3? e5! and Nf3 must get stoned.

Strange game. If you threaten to capture something, it can stone you; if you threaten to stone something, it can capture you. How can you make progress?

The Simplest One is Best

Whether or not you liked it, at least I found this train of logic interesting to follow.

My wonderful idea of the Gorgon? I went to all the trouble of working out the details and now I don't like it. Bummer.

The idea of Hydra Chess (Deferred Direct All FIDE Capture) is nifty, but the game might not be good to play.

Deferred Inverse One AutoRifle could be a good game, but I think it would not be to my taste.

Several other new games were described, but out of all these interesting ideas, the only one that's a really great and playable game is the simplest one of all, the first one I mentioned, simple Inverse Capture Chess.

I guess it's the season for inverse capture.


By the way, if it is only one Queen occupying 3 squares, how do you move it?

The answer is found in Tirebiter Chess.


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