keep a knight from being strongly placed, or destroy the kings pawn cover and remove a defender. A common example of this occurs in the Sicilian when Black exchanges a rook for knight in order to continue his attack on the queen side. FEN=2r1k2r/1b1b1ppp/p2p1n2/qp2pP2/1N2P1P1/P1NB4/1PP1Q2P/2KR3R b k - 0 1 16... Rxc3