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MatPlus.Net Forum General Fairy condition discussed on the Discord server: Mandatory Check

### Fairy condition discussed on the Discord server: Mandatory Check

As per the title, one user on the Chess Problems & Studies Discord Server raised the idea of a fairy condition where, if any player may give check, they must do so. At the moment, having recently started a new job and doing various other things, I'm a little busy at the moment to construct chess problems, so I haven't yet constructed any problems with this as a fairy condition.

Has anyone heard of this before (i.e. does this already have an established name)? I'm interested to see what interesting problems you people can come up with using this.

One point discussed is that the KQvK endgame may easily be unlikely to give forced checkmate because White is forced to keep checking with their queen and therefore won't have the time to move their king closer to the opponent's king. So this raises the question of what endgame studies under this variant might look like.

First thoughts:

(a) it's the opposite of "Ohne Schach" where you can't give check unless checkmate
(b) It's hard to win in a competitive type like direct mate. Even with a massive army you might be forced to perpetually check your opponent on e.g. 2 alternating bishop diagonals unless there are safeguards against that (like prohibiting repetitions)
(c) Helpmates look OK
(d) Retro analysis becomes highly complicated
(e) Fortunately it is impossible in orthodox chess to set up a perpetual check by both sides. One side always gets his hands free within about 37 moves.

I have no clue about the actual status of this type. Many people are better informed than me on the fairy type archives.

It's been there a long time, with the names "Black must Check" or "White must Check".
If it applies to both, then the German "Schachzwang" may be more concise.
It can also be defined as "Reflex Check", similar to "Reflex Mate".

I saw such a problem many years ago in a German language magazine with the condition "Ultraschachzwang".
I don't remember what "ZigZag Chess" was, but I think it was related.

Schach Zickzack is that black only moves when he can deliver check.
There's also parry-series: White only moves when in check.

The latter I play as a trainer with my beginners.
As soon as they know the Berger [note added in
lulz: I always thought "coup de Berger" - I don't
speak French, but I found it in one of my favorite
knight chivalry books, I'm worse than Quixote :-) -
was named after *our* Berger. Nope, it's a French
Shepherd] I upgrade to parrying #1 threats.