Chess invariants • Hacker News Board

Re: Chess invariants

#21

Post by [deleted] » Fri, May 22, 2026, 1:43 PM UTC

[deleted]

Re: Chess invariants

#22

Post by nonethewiser » Fri, May 22, 2026, 1:50 PM UTC

rauljara wrote: post #13

Anyone know what language is being used in the blogpost?

TLA+ i think

Re: Chess invariants

#23

Post by emil-lp » Fri, May 22, 2026, 1:58 PM UTC

munchler wrote: post #10

JohnKemeny wrote: post #4

Earlier quoted context omitted.

Well, if a piece is pinned it's illegal to move it. Rule 3.9.2: No piece can be moved that will either expose the king of the same colour to check or leave that king in check.

The point is that, logically, the first part of that rule (“expose the king”) is implied by the second part (“leave that king”), so the first part is redundant. You could simplify the rule to: No piece can be moved that will leave the king of the same color in check.

You should submit it to FIDE.

Re: Chess invariants

#24

Post by saberience » Fri, May 22, 2026, 2:13 PM UTC

JohnKemeny wrote: post #4

yewenjie wrote: post #3

> Chess is a lot trickier than it looks. It has so many rules: castling, en passant, pawn promotion, pinning, the discovered check, and the deadlock case of stalemate. Nit: Pinning and the discovered check are not really rules, but rather names of tactics.

Well, if a piece is pinned it's illegal to move it. Rule 3.9.2: No piece can be moved that will either expose the king of the same colour to check or leave that king in check.

Pinning isn’t a rule, it’s just something that arises from other rules.

Also, pinning can happen with pieces that don’t include a king, which means you can just move out of the pin and expose whatever other piece.

It’s just a chess tactic, not a rule. It’s like saying a chess skewer is a rule too.

Re: Chess invariants

#25

Post by anamexis » Fri, May 22, 2026, 2:30 PM UTC

333c wrote: post #11

JohnKemeny wrote: post #9

Earlier quoted context omitted.

3.9.2: no piece can be moved if that exposes or leaves its own king in check.

That's a consequence of not being allowed to put yourself in check (by any means).

The only way to put yourself in check is by moving.

Re: Chess invariants

#26

Post by 333c » Fri, May 22, 2026, 2:39 PM UTC

anamexis wrote: post #25

333c wrote: post #11

Earlier quoted context omitted.

That's a consequence of not being allowed to put yourself in check (by any means).

The only way to put yourself in check is by moving.

Did you mean putting your opponent in check? In chess, you are not allowed to put yourself in check.

Re: Chess invariants

#27

Post by yifanl » Fri, May 22, 2026, 2:46 PM UTC

anamexis wrote: post #25

333c wrote: post #11

Earlier quoted context omitted.

That's a consequence of not being allowed to put yourself in check (by any means).

The only way to put yourself in check is by moving.

The only action you can ever take in chess is moving.

Re: Chess invariants

#28

Post by anamexis » Fri, May 22, 2026, 2:55 PM UTC

333c wrote: post #26

anamexis wrote: post #25

Earlier quoted context omitted.

The only way to put yourself in check is by moving.

Did you mean putting your opponent in check? In chess, you are not allowed to put yourself in check.

You said “ That's a consequence of not being allowed to put yourself in check (by any means).” My point is that there are no other means.

Re: Chess invariants

#29

Post by nilslindemann » Fri, May 22, 2026, 2:58 PM UTC

I read these images of source code the same way as I read images of math formulas on Wikipedia: Not at all.

Re: Chess invariants

#30

Post by vunderba » Fri, May 22, 2026, 3:07 PM UTC

> Chess is a lot trickier than it looks. It has so many rules: castling, en passant, pawn promotion, pinning, the discovered check, and the deadlock case of stalemate.

As a kid playing chess with other neighborhood kids back in the day, absolutely none of us even knew about the en passant rule. My first exposure around the same time was completely by accident thanks to a passing reference in a CRPG called Betrayal at Krondor. It comes up in a story about a game that nearly costs an innkeeper her establishment when she loses because of a move she didn’t even know existed.