This is a screenshot from a chess.com tutorial.
In the final sentence it says,
White will often gain the bishop pair after 5. a3, with a sharp struggle ahead.
Obviously a3 is the pawn attacking the bishop which is pinning the knight, but I'm missing what "bishop pair" means. Assuming that bishop on b4 is one of the pair, does it mean:
- A pair of bishops, in which case which is the other bishop, and where is the gain?
- The bishop and pinned knight form a pair, which will be traded via Bc3 then bxc3, in which case, again, where is the gain? Black has destroyed the pawn structure, but not gained material. Besides, the text says that white makes the gain, not black.
- The black bishop retreats from the pawn, and somehow white makes a gain from it. In which, please help me see that sequence. Does white gain two bishops?
- Something else? Perhaps "bishop pair" is an idiom?