Smyslov Variation

The Smyslov Variation answers 5. a4 in the Slav with 5...Na6, heading for b4, the square loosened by White's a-pawn advance. Black concedes the center to 6. e4, the most common reply, or 6. e3. In return Black seeks counterplay with ...Bg4, pinning the f3-knight, as in 6. e4 Bg4 7. Bxc4 e6 8. O-O Nb4. Smyslov popularized it in 1959. It now serves mainly as a surprise weapon, and engines give White a slight edge.