Chess puzzle (Advantage)
Moves: 1. d4 d5 2. Bf4 Bf5 3. e3 e6 4. Nf3 Nd7 5. h3 h6 6. c4 c6 7. Qa4 dxc4 8. Bxc4
Nb6 9. Qb3 Nxc4 10. Qxc4 Nf6 11. Ne5 Bd6 12. Nxc6 Qc7 13. Bxd6 Qxd6 14. Ne5 O-O
15. O-O Rac8 16. Qe2 Rc2 17. Qb5 a6 18. Qb3 Rfc8 19. Nc3 b5 20. a4 *
Position (FEN): 2r3k1/5pp1/p2qpn1p/1p2Nb2/P2P4/1QN1P2P/1Pr2PP1/R4RK1 b - - 0 20
Black to move.
Themes:  Middlegame  
Puzzle rating: 1677
Best move: b4