Comments by azgoroth

It's clear that the rules of compulsion as laid out here are not quite formal. I took my own stab at interpreting them on the itch.io page that I linked. To summarize my interpretation:

• Every compulsion defines conditions under which it is satisfied.
• Multiple occupancy compulsion is satisfied by moving off or destroying the piece entirely (plus some edge cases).
• Ichor compulsion is satisfied by moving off, being pushed to a non-ichorous square, or destroying the piece entirely (plus some edge cases).
• Ghast compulsion is satisfied by fleeing, being pushed further from the Ghast, destroying the Ghast, or destroying the piece (plus some edge cases).
• If it's your turn and one of your pieces is compelled, you must make a legal move that satisfies at least one of your pieces' compulsions.
• There is nothing wrong with adding new compulsions to your pieces, although this is only possible with either a Go Away's push or by a Wounded Fiend leaving a square containing another one of your pieces.

While typing this up I realized that there are a few omissions in my edge cases, which I will rectify when I get a chance. It really is tough to enumerate all the cases!

The observations that certain pieces become effectively neutral in color on petrification, and that a petrified Go Away is identical to a Mummy, are almost true. However, if one were to actually make such reductions during play, information would be lost as far as counting repetitions of positions goes.

Unrelated but worth mentioning while I'm here: in my Nemoroth implementation, there are really two Leaf Pile piece types, normal and "digesting." A normal Leaf Pile becomes a digesting Leaf Pile upon engulfing a piece, and a digesting Leaf Pile reverts back to normal when it moves of its own accord (i.e. not as a result of a Go Away's scream). It's rather important to keep track of this state, or you won't remember whether the Leaf Pile is supposed to leave behind a Mummy. This is an unfortunate omission from the otherwise fine scheme in the "Nemoroth Notation" article by John Lawson -- I would suggest using a "d" prefix to indicate digestion, such as in "dL."

Just over twenty years after the initial publication of this page, the first ever computer implementation of Nemoroth is live, complete with a basic alpha-beta pruning AI. You can play in your browser at this link: https://azgoroth.itch.io/nemoroth

The only thing I haven't implemented is the Go Away push order, which I've been putting off due to how laborious the UI considerations are. As a placeholder, Go Away pushes are clockwise from top.

I originally wrote this implementation in TypeScript, but the AI was too slow and I ported it over to C++ using WebAssembly. I plan on open sourcing it eventually once I have more opportunities to clean up the code. This is one of the most difficult software projects I have ever worked on; I have known about Nemoroth since around 2013 but was not a strong enough of a programmer to pull it off until now.

I found a number of ambiguities in these rules, which I have tried my best to address reasonably on the linked page. Some have been covered in this comments section, some not (for example, if a Wounded Fiend leaves an already ichorated square, does the ichor stack to 11+ plies or max out at 10?).

The AI is surprisingly dangerous. It mobilizes the Ghast immediately and WILL advance it to d4/d5 if you let it, usually costing you the game. I have managed to beat it a few times, but it's tough as nails for how crude the programming is. Beware!

Ralph, if you're out there, thanks for this amazing variant. I tried to email you to get permission to make this but alas, I never heard back.