Chess puzzle (Advantage)
Opening: Queens_Gambit_Declined, Queens_Gambit_Declined_Queens_Knight_Variation
Moves: 1. d4 d5 2. c4 e6 3. Nc3 Bb4 4. a3 Ba5 *
Position (FEN): rnbqk1nr/ppp2ppp/4p3/b2p4/2PP4/P1N5/1P2PPPP/R1BQKBNR w KQkq - 1 5
White to move.
Themes:  Opening  
Puzzle rating: 1834
Best move: b4