with Bf5

After 1. Nf3 Nf6 2. g3 d5 3. Bg2 c6 4. O-O, Black answers with 4...Bf5, bringing the queen's bishop outside the pawn chain before closing it in with ...e6. The resulting arrangement, with pawns on c6 and d5 and the bishop on f5, amounts to a London System with colors reversed. It addresses the main drawback of the ...e6 lines against the King's Indian Attack, where the c8-bishop often stays passive. In return, the bishop can become a target, and White's choice of plan decides how much that matters.

The most frequent reply by a wide margin is 5. d3, preparing Nbd2 and e4, when the advance of the e-pawn gains time against the f5-bishop and keeps the game in typical KIA territory. 5. c4 instead pressures d5 from the flank in Réti fashion and gives White slightly the best results among the main moves, while 5. d4 stakes a direct claim in the center. Engines also consider 5. Nh4, chasing the bishop at once. Engines give White a slight edge, and White scores somewhat better than Black in online play.