White can defend the pawn at c4 with a piece by playing 5.Nbd2, 5.Qa4, 5.Qc2 or 5.Qb3, but these moves all diminish control of d4, making ...c7–c5 an effective reply for Black; therefore 5. b3 is White's most common response. However, it weakens the dark squares slightly, which Black can take advantage of by playing 5... Bb4+. Now 6.Nbd2 loses material after 6...Bc3 7.Rb1 Bb7 threatening 8...Be4, an opening trap which has ensnared players such as Kamran Shirazi. White's best move is therefore 6. Bd2. However, after 6... Be7 7. Bg2 c6 Black is ready to play ...d7–d5, again attacking the c-pawn. If White plays cxd5 then ...cxd5 is considered to for Black. Thus White usually plays 8. Bc3 to clear the d2-square, and after 8... d5 White can play in two ways. After 9. Nbd2 Nbd7 10. 0-0 0-0 11. Re1 c5 Black has achieved his thematic before White and the resulting position after 12. e4 dxe4 13. Nxe4 is equal. Therefore, the main line continues 9. Ne5 and since Black does not want White to maintain this knight on a strong central outpost, play continues 9... Nfd7 10. Nxd7 Nxd7 11. Nd2 0-0 12. 0-0 Rc8 13. e4. By diverting the black knight on move 9 it is now White who has achieved his central pawn break first. The effect of Black's check 5...Bb4+ has been to lure White's bishop to c3 where it blocks the c-file. This, the current main line of the Queen's Indian, is considered equal by theory and became a frequent guest in grandmaster praxis in the 1980s.