Invaders and helpers
Black to move 1k6/1b3p1p/p7/3qp3/Np5Q/4BP2/PPP3rP/R4K2 b - - 1 26 Jean-Marc Degraeve vs. Laurent Guidarelli (2003) Source Chessable The Checkmate Patterns Manual The black queen and bishop cooperate to invade f3 Once invaded, a new invasion square emerges: The black rook and queen eye to f2 But that focal point is defended by the white queen and bishop After 1. ... Qxf3+ 2. Bf2 the helper black rook sacrifices itself 2. ... Rg1+ and acts as a magnet to attract the white king to another square White gives mate from one of the two invasion squares g2 or h1 The invasion squares are clearly dynamic, and move with the pieces