delays castling so as not to come under attack there. If Black wants to transpose into the Byrne while avoiding the 7.Bd3 lines, the flexible 6...a6 can be played first. This way, Black retains the option of playing ...c5 or ...c6 depending on the circumstances. Panno Variation: 6...Nc6 The Panno line, named after Oscar Panno, is a sharp and highly theoretical system which can lead to very complicated play. Black holds back the c-pawn for the time being, and aims to put the knight on d4. The immediate plan is to prepare queenside counterplay with ...a6, ...Rb8 followed by ...b5. The main line of the Panno is 7.Nge2 a6 8.Qd2 Rb8. White's main positional system is to continue with 9.Nc1 e5 (Black needs to secure a hold of the centre) 10.d5 Nd4. Here the pawn grab 11.Bxd4? exd4 12.Qxd4 loses to 12...Nxe4!, so White usually challenges the d4-knight with 11.Nb3 or 11.N1e2. Other seventh move alternatives include the aggressive continuations 7.h4 and 7.g4 aiming for a kingside attack, and 7.Rb1 and 7.Rc1 which aims to meet the ...b5 break. Other lines against 6.Be3 6...Nbd7 was popular in the early 1990s. Cherniaev and Prokuronov, however, believe White obtains an edge with 7.Nh3, with the plan of bringing the knight to f2. 6...a5 is a line favoured by Mark Hebden. The idea behind the move is to advance the a-pawn down the board to a4. Spending two tempi on pushing the pawn to a4 costs time, but Black has secured the a5-square as a comfortable perch for the queen, and the advance a4–a3 may come up later in the game. 6...b6 was once played as a means of preparing the break with ...c5, but since the Sämisch gambit shows that 6...c5 can be played immediately, Chris Ward considers the line to be slightly inferior. Other sixth moves for White Since the Sämisch gambit shows that 6.Be3 does not really prevent 6...c5, some players have turned to alternatives. These alternatives include 6.Nge2 which postpones the decision of where to put the c1-bishop, and 6.Bg5 aiming for a more active development and preventing 6...e5? due to the pin after 7.dxe5 dxe5 8.Qxd8 Rxd8 9.Nd5. Sidelines Although most lines in this variation have Black castling at move five, it is certainly possible for Black to delay castling, even to junctures well into the middlegame. A rare move such as 5...c6 holds Black's options open while