Bishop X-ray threats
Idea from Gary Linscott. Tuned for DiscoCheck by me (lots of games).
The more natural and general idea is to penalize pins more generally, but with other pieces than bishops there are may annoying exceptions to consider, and it doesn't work as well (as shown by Gary's experiments in SF).

8000 games in 10+0.1
2165-1876-3959 [51.8%] LOS=100.0%

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