B43 Sicilian Defence: Kan

After 1.e4 c5 2.Nf3 e6 3.d4 cxd4 4.Nxd4 a6, the Kan (or Paulsen) Variation of the Sicilian Defence, this code covers White's most natural reply, 5.Nc3, which develops a piece and keeps c2–c4 in reserve. Black's ...a6 stops a knight or bishop from using b5 and prepares queenside expansion. With 5...Qc7 Black watches e5 and delays committing the kingside pieces, and play often continues 6.Bd3 Nf6 7.O-O. The sharper 5...b5 gains queenside space at once and readies ...Bb7 against e4. After 6.Bd3, the move 6...Qb6 hits the knight on d4.