Where can the combined Bishop/Pawn (Biawn) on b2 move?
Solution: The Biawn can move as the Bishop or the Pawn.
Biawn moves forward as the Pawn to b4.
The notation for this is: BPb4
the Biawn can split, and the Pawn or the Bishop can move away.
Here the Bishop splits and moves to e4 leaving the Pawn behind. (notation Be5)