a bishop whose mobility is restricted by own pawns. As opposed to normal mobility problems, this situation is semi-permanent (more so if the position is blocked), which fact justifies singling it out as another evaluation term. Bad bishop is not such a liability if it is placed outside the pawn chain (Bf5 in the Slav). For that reason some programs, like Crafty, score a bishop as bad only if its forward mobility is impaired.
For a bitboard-based program a feasible approach would be to create an array of 64 bitboards, indexed by a Bishop's position, and marking the pawn positions which would make our bishop bad.
- Matej Guid, Martin Možina, Jana Krivec, Aleksander Sadikov, Ivan Bratko (2008). Learning Positional Features for Annotating Chess Games: A Case Study. CG 2008, pdf
- Evaluating bad bishops by Tord Romstad, Winboard Programming Forum, May 15, 2006
- Bad/good bishops in R3 and IPPOLIT/IvanHoe by Mark Watkins, Open Chess Programming Forum, November 30, 2010
- Good bishop and bad bishop from Wikipedia
- How Bad is a Bad Bishop? by Iryna Zenyuk, Chess.com, February 27, 2019
- The Bishow's Show: Bad Bishop by Iryna Zenyuk, Chess.com, March 09, 2012