Example from Robert

 Robert uses the same book as me, which is handy because I have seen the problem before.

White to move

6k1/4brpp/r1p1pp1B/p3q3/2P1N3/PP4Q1/2n3PP/3R1R1K w - - 0 22 

Orange square - target. Targets are pieces or PoPs (points of pressure) that lie on the LoA (line of attack) from attacker to piece. f8 is a bit surprising, but it is on the LoAs from the white roos towards the black king. They converge on f8.

Red circle - defender. Piece with a function.

The defenders are restricted in their movements. By forcing the defenders to fulfill their duties you can win a crucial tempo that makes the combination work.

22.Nf6+ Bxf6  now the bishop has a double function. Or actualy a triple function:

• it must defend the invasion square d8
• it must defend Qe5
• it must keep the f-file closed

23.Qxe5 Bxe5 make use of the overloaded black bishop. The invasion square d8 is no longer defended.

Notice how the white attack follows the change of functions. Essentially, white has won a tempo here due to the double attack on e5 en d8, while black can defend only one.

24.Rd8+ Rf8 25.Rdxf8#

Notice how the function and tempi dictate the moves by logic.