King's English Variation, Four Knights Variation, Korchnoi Line

The Korchnoi Line, 4. a3, spends a tempo to rule out the ...Bb4 pin, one of Black's main resources in the Four Knights. It can also prepare b4 to gain queenside space, a reversed version of the Sicilian ...a6 idea with an extra move in hand. Black most often replies 4...d5, breaking in the center at once. 4...Bc5 and 4...a5, which restrains b4, are the other common choices. The engine rates the position as roughly balanced.