# Is a both-sides forced perpetual check possible?

There are lots of positions where one side can force the other into a perpetual check. Is there any position in which there are no legal moves besides continuing the perpetual from both sides? For example, let’s say White is checking Black. Black has to move due to the check. Then, White somehow has no other legal move than to continue the perpetual.

I am asking purely out of curiosity. I don’t think such a position would be likely to be reached in a real game Ideally, there would only be pieces on the board that are attainable in a real match though, e.g. no 10th queen. I am also interested if it’s possible to prove that there is no such position.

• This is a duplicate, methinks (i.e. I'm fairly sure it has been done either here or on Math SE, with a solid proof, by Noam Elkies I think, but am too lazy to google :-) See also chess.stackexchange.com/questions/8982/… for additional info. Sep 26, 2021 at 8:04
• @HaukeReddmann when you say it "has been done", do you mean that it has been proved to be impossible? Sep 26, 2021 at 18:43
• @JamesMartin: So I think, but be careful. At least the "proof" in the link is incomplete, and moreover a fairly simple fairy piece, the camel (1:3 knight), makes a mutual perpetual possible (same link). Thus it must be proven that knights can't be used in the same way. Sep 26, 2021 at 19:37
• Further note the original poster asks for a forced perpetual, which is even harder (the camel solution fails because the battery hind pieces can interlope, and if you pin them, even if that is possible at all, the pinner can capture and must be pinned too). The "proof" in the link probably can be amended to take care for that. Sep 26, 2021 at 19:42
• @HaukeReddmann I have to say I'm confused. Any proof in the link you gave doesn't seem relevant, since that question asks about consecutive checks by both players, whereas this question only requires a sequence of checks by one player. I'm not sure it's a good idea to say that it's a duplicate, unless you can point to where the answer is - it seems a bit unfriendly to a first-time poster.... Sep 26, 2021 at 20:54