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ChessXp. 10x10 Chess, strictly derived from the 8x8 architecture.[All Comments] [Add Comment or Rating]
Jean-Louis Cazaux wrote on 2021-08-24 UTC

I like this variant. Not original of course, but I don't care. I'm not fond of those who patent their CV "invention", I think it is presumptuous and quite inefficient for what they are looking for. In the case of Falcon Chess, it seems to me that the patent is exhausted for not renewing the fees.

Anyway, ChessXP is quite simple and well designed. The position of the CZ is optimal. The rules for Pawn's move is clever. About the name of the CZ, I would have preferred that the tradition of Bison (yes, at least from 1974 and probably older among problemists) is kept. There are too many Falcons/Hawks/Ospreys already, for example Schulz's Falcon in Hunter-Falcon chess in the 40s (fBbR), Hawk of Musketeer chess (ADGH), another one in Seirawan chess, etc. Why departing from the Bison?

Apart from that, very good!

Andrew L Smith wrote on 2021-08-23 UTCGood ★★★★

This seems like a nice variant. I especially like the 32221111Q movement of the pawns. The falcons/bison are also fun to play with, their long leaps make for nice tactics.

Pretty much the only thing I'd change is that castling leaves the King too close to the middle. Instead, I would make it so that castling results in the King and the Rook swapping places (White king can go to b1 or i1, black king can go to b10 or i10; rook always goes to the f file) as this gets the King 1 space away from the corner. This would also fix one of the gripes I have with regular chess: queenside castling is usually terrible. Opposite side castling often leads to fun games, so making it happen more often seems like it would be desirable. Also, it would allow players to castle by moving the Rook first, as the ambiguity between O-O and Rg1 is removed.

Bn Em wrote on 2021-03-15 UTC


Re Duke's variant and patent: whilst it was, indeed, probably an exercise in extending the patent's scope, I'd argue that technically he did describe this variant first (and strictly speaking patents are a different thing from copyright, and I'm not convinced that someone patenting a new set of chords (perhaps in some unusual tuning?) that wasn't in prior use coudn't in fact claim a breach of patent on anything using them, though ofc IANAL) — however you rightly point out that he came to different conclusions, and that merely having described it as part of a set of possibilities doesn't mean that he should be credited for it (H. G. Muller's analogy with integers is apt here). My main point was that it's more interesting (at least for me ☺︎) to acknowledge the commonalities (as you have now, indeed, done) and explore the differences within that than to insist that everything is unique and special in itself.

Also I agree, naming things is hard (which is partly why it was uncanny that you ended up with the same name as Duke did).


Strictly speaking Kestrel has been used (by Gilman, predictably enough) for a piece — just not in any games. It's the compound of (stepping) Falcon and Kite (the latter moving as falcon but replacing orthogonal steps with ‘nonstandard’ (i.e. √3) diagonal ones) according to M&B13.

Uli Schwekendiek wrote on 2021-03-15 UTC

@Fergus Duniho

Thank you very much for approving my submission.

I admit the name collision is not an ideal situation. While working on this project, it occurred to me that naming is the hardest part, not programming or figuring out the rules. Regardless of whether you are looking for a domain name, a game name or a piece name, the obvious and even the most non-obvious solutions are already taken.

As you and @Bn Em already pointed out, the piece naming system is partially broken. Since the Bison/leaping Falcon is an important piece for building game variants close to classical chess, this is probably a good opportunity to revise this part of the nomenclature.

I added a "buildings blocks" section to my paper where George Duke is given credit for the commonalities shared by both specs.

@Jörg Knappen

Many thanks for your suggestion, but I suspect that if this variant should ever get a community, people would not really embrace this name. too far away from first choice solutions.

Fergus Duniho wrote on 2021-03-15 UTC

Okay, I've unhidden this.

Jörg Knappen wrote on 2021-03-14 UTC

While I think that the inventor of a Chess Variant has the final say in the naming of pieces, I must admit that the choice of Falcon is a very unfortunate one because the Falcon of George Duke's Falcon Chess is vexingly similar to that piece but different.

What about naming it Kestrel (in German Turmfalke instead? This keeps most of the semantic associations but uses a free word (not used for a chess piece yet as far as I know).

Uli Schwekendiek wrote on 2021-03-14 UTC

@Fergus Duniho

I would like to stay with falcon. It is the most logical name for a flying piece in chess, since falcons are the birds of kings in many cultures and stand for aggressivity, dynamics and speed. Hawk or eagle would be alternatives, but they are not as precise.

Another cuddly option would be terror bird (t-bird). Could not fly and was - according to recent discoveries - probably plant eater. Like the bison.

@Bn Em

Dukes spec/patent settles clearly for a 8x10 board, a non-leaping falcon and a rnbfqkfbnr setup. He mentioned a 10x10 board as one of a bunch of variation possibilities, probably to broaden the claim his patent covered, along with chinese pawns and the giraffe piece. But that's not a spec. That's simply numbering a list of items. Or to put it another way: You can't list a number of chords and claim copyright for every song that's written with this chords.

A commonality of both specs is to minimize the necessary rule adjustments compared to classical chess and to extend the b, n, r line with the next logical piece. However, in both cases he came to different conclusions than I did.

Btw, tells us that the bison was used as early as 1974.

Bn Em wrote on 2021-03-12 UTC

Agreed that it's not exactly the same, and taking the motivations into account there are some noticeable differences, merely very similar — especially since iirc Duke explicitly mentions the leaping falcon (i. e., indeed, the Bison) and 10×10 board as (rejected, in his case, but possible as subvariants) alternatives and the setup with falcons in the corners is his second favourite according to the comments on that page. Honestly I mostly just find it interesting that much of it seems to have been reinvented independently — suggests that, for all his self‐importance (patenting a variant? Really?), he (and, indeed, you) may have been onto something.

It is a bit of an odd artifact that leaping pieces tend to be named after non‐leaping animals: Camels, Giraffes, Bisons, Buffaloes… while the piece with a bird's name (the rook — indeed even in Japanese the ‘Flying’ Chariot) is among the most easily blocked, at least of the orthodox set.

I don't see as great an issue with the Falcon name clash though; after all we don't distinguish leaping and stepping elephants, dabbabas, ⁊c., or Chinese and (albeit much less popular) Korean cannons by name. And since the name is also used for the forward‐bishop/backward‐rook piece…

Fergus Duniho wrote on 2021-03-12 UTC

Please, I don't want to name it Bison ...

Bison is probably a bad name for the piece, since that animal doesn't look like much of a leaping animal at all. The main point I want to make is that Falcon is already the established name for the non-leaping counterpart to this same piece, and calling the leaping version a Falcon could sow confusion. So, I would recommend picking a different name.

Uli Schwekendiek wrote on 2021-03-12 UTC

@Fergus Duniho

Thanks, upload worked now!

Please, I don't want to name it Bison ...

@Bn Em

I don't think that it is exactly the same concept. Different board size, different extra piece (leap), different pawns, different setup. Falcon is simply a cool name for such a piece and relates to the eastern mythology.


Against an undeveloped position, the falcon can force a precise defense early on. For example, after 1.Fc4 black has probably only one reasonable answer: 1. ... e6. This might be ok, since there are many situations in chess where the defender has only one working defending move, but nevertheless a good (if not a winning) position. And I doubt that an early bird has real advantages except threatening fools mate.

A first move block for the falcon would be necessary for a shuffled setup comparable to Fischer-Random, since an early bird can be an instant win here, depending on the initial placements of the falcons. I built in this rule for a point symmetric setup. See

From a developed position, an enemy falcon is pretty manageable, according to my experiences.

I took out the falcon-rook comparison from the spec and leave a proper estimation of its strength to further tests.

@Greg Strong

I didn't know that such an engine exists. That's pretty cool, I'll check it out.

Greg Strong wrote on 2021-03-12 UTC

It seems ok. I let chessv think to depth 19 and it only considers white to be up 1/10th of a pawn.

H. G. Muller wrote on 2021-03-11 UTC

The Bison is indeed much stronger than a Rook; leapers with 16 targets are typically worth 7-8 Pawns. The fact that these are leaps of range 3 makes it extra dangerous. In fact, I couldn't test Bisons as piece replacements in a FIDE setup, as it made the position non-quiet. Too many unprotected pieces on the back rank a Bison can attack with impunity. I suspect there could be the same problem here: after 1. Fh4 black already faces a mate threat. The white advantage here could be enormous (on the order of a Rook). I would have to analyze it with Fairy-Max to be sure.

Fergus Duniho wrote on 2021-03-11 UTC

The more common name for the leaping counterpart to the Falcon is the Bison.

Bn Em wrote on 2021-03-11 UTC

This bears an uncanny resemblance, even down to the name chosen for the extra piece, to George Duke's Variant, though the pawns' multi‐step move is novel afaict.

That game's non‐leaping (‘multi‐path’) falcon was measured as being a little more valuable than a rook (albeit on 8×10), so I wouldn't be at all suprised for the leaping one to be more powerful yet.

Fergus Duniho wrote on 2021-03-11 UTC

Try your upload again. I fixed the problem Ben was having, and it is likely the same problem you were having.

Email is not as reliable as it used to be, thanks to many email services cracking down hard on spam email. That's why you no longer need to verify your email to sign up.

Uli Schwekendiek wrote on 2021-03-11 UTC

I tried to replace the external image links with local ones, but uploading an image failed with

"Upload of /home/chessvariants/public_html/membergraphics/MSchessxp/bnfrcomparison.png was allowed but failed! The cause of failure is unknown."

Verifying my mail adress didn't work as well, I didn't receive anything from [email protected]

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