31 ... Nb6-c4 shields the backward Black c6-pawn on open c-file Korchnoi vs Karpov, 1978  (D37) Queen's Gambit Declined, 61 moves, 0-1 19 ... Nbc4 Black c4-knight shields c6-pawn on the open c-file P Nikolic vs Kramnik, 1998  (D43) Queen's Gambit Declined Semi-Slav, 35 moves, 0-1 24 ... Ncd4 shields backward Black d6-pawn on the open d-file J Werle vs Bologan, 2007  (E97) King's Indian, 53 moves, 0-1 24 Nb2 White plans Nb2-c4, blocking c-file to backward c2-pawn Tarrasch vs Alekhine, 1923  (C60) Ruy Lopez, 54 moves, 0-1 4 games