Chess puzzle (Advantage)
Opening: Queens_Gambit_Declined, Queens_Gambit_Declined_Harrwitz_Attack
Moves: 1. d4 d5 2. c4 e6 3. Nc3 Nf6 4. Bf4 c6 5. e3 Bd6 6. Bg3 O-O 7. Nf3 b6 8. cxd5
cxd5 9. Bd3 Bb7 10. Rc1 Nc6 11. a3 Na5 12. Bxd6 Qxd6 13. O-O Rfc8 14. Ne5 Nc4
15. Nb5 Qe7 16. Nxc4 dxc4 17. Bxc4 *
Position (FEN): r1r3k1/pb2qppp/1p2pn2/1N6/2BP4/P3P3/1P3PPP/2RQ1RK1 b - - 0 17
Black to move.
Themes:  Middlegame  
Puzzle rating: 1994
Best move: a6