Atomic implementation incorrectly declares stalemate

In the Atomic ruleset that I know, the ending position of this game is not stalemate: lichess.org/ChiICzuitKTJ

The Atomic ruleset I know doesn't have a notion of check, so it's not illegal for a king to walk into check. The Atomic implementation on Lichess appears to forbid a king from walking into check, with some conditional logic to allow a king to be in check if it's adjacent to the enemy king.

This usually gives the same outcome... except for the edge case where a king is adjacent to the enemy king, and its only legal moves are both (1) into check and (2) not adjacent to the enemy king.

thats because the enemy king is next to your king. so taking that enemy king would blow your king
too so its not allowed.

Huh, it seems that there are multiple Atomic rulesets out there. For example, the ICC ruleset doesn't have a concept of check at all. Wikipedia mentions multiple rulesets that disagree on how to treat check and stalemate.

So maybe what I've found is just a corner case where the rulesets disagree. And if Lichess knows this and wants this version -- i.e. this is a feature, not a bug -- then all right. I still find that, at least in the spirit of the rules, it's quite counterintuitive for this position to be stalemate.

Curious to have an admin weigh in on this.

You can find the Atomic Rules for Lichess here: lichess.org/variant/atomic

You cannot move your King into Check after those rules (which are the original ones from the 90s I think)

Chronatog mentions on his Website about the History of Atomic that ICC does differ from the standard rules: chronatog.com/2019/07/atomic-on-icc/

I did my best in collaborating with other Lichess developers to correctly define and implement rules for these corner cases. When kings are adjacent, there is no check.

this study is a reference ruleset, I think it is inherited from FICS, not ICC.

The incorrect rule implementation actually occurred when introducing atomic (or wild 27) to ICC some 20 years ago. Prior to that, as well as on most other sites since, atomic chess has had check and stalemate.

It's quite complex but that is stalemate for the following reasons:

A king can never capture anything, and the black king cannot move to either of the two adjacent squares as then it would be in check. Black also has no other pieces.

The black king is not in check now, because if it were white's move he would not be able to capture the black king (without blowing up his own).

Therefore black has no legal moves and he isn't in check, so it's stalemate.