Triangulation is a tactic used in chess to put one's opponent in zugzwang (a position in which it is a disadvantage to move).
Black's king must stay close to where it is; he must prevent the c-pawn from advancing, and he must not let himself be driven to the edge of the board.
White can win by the following maneuver: and now the triangulation is complete and we have the same position but with Black to move.
In this 1978 game between Lev Alburt and future World Champion Garry Kasparov,[3] Black wins by triangulating: and White resigned.
This position (from analysis of a game between Alexey Shirov and Alexander Grischuk in New Delhi in 2000) shows an example when the kings are far apart.
[9] In this game between future FIDE World Champion Veselin Topalov and former world champion Anatoly Karpov,[10] White triangulates with his rook to put Black in zugzwang: back to the same position and Black is in zugzwang.