PINS AGAINST FLIGHTS: WHEN YOU MUST MEET A THREAT BY STEPPING ONTO THE LINE OF AN ENEMY LINE PIECE

L Christiansen vs Nunn, 1991

Black must meet 36 Ne7-g6+ with 36 ... Kf8-f7, stepping onto the line of the White h7-queen. <WITHOUT THE BLACK g7-bishop MAKING A TUNNEL FOR THE BLACK f8-king ON THE f7-sq, 36 Ne7-g6+ WOULD BE MATE!>. So the Black g7-bishop *must* <INTERPOSE> the f7-square hence it cannot also <PROTECT> the Black f6-pawn. 36 ♖f1xf6+! 1-0 as the Black g7-bishop is <PINNED> against the f7-flight sq; 36 ... ♗g7x♖f6 means <THE TUNNEL HAS CLOSED>, meaning that the f7-sq is no longer a <FLIGHT> for the Black f7-king, so 37 ♘e7-g6# is now checkmate.

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Also see the <IM OSTROVSKY BANTER BLITZ VIDEO> where he plays the same idea with a <KNIGHT FORK>.