[eru]

Thanks!

> relaxing and omitting chess rules also changed the choice of variables.

I wonder if you can recast some of that in terms of (dynamic) row generation?

> I did try lazy constraints etc. before diving into the math, but they did not yield a significant speedup.

Yes, I can believe that. My point wasn't so much that using heuristics like these is somehow bad, but more that the off-the-shelf solvers can be made to cooperate with (many of) your heuristics.

> For example, not considering the white king as being in check simplified A LOT.

I guess you could classify that as branch-and-bound, if you squinted really hard?