Crossword Genius

According to the rules (2,3,4)

Ross

I believe the answer is:

by the book

'according to the rules' is the definition.
(I've seen this before)

This is the entire clue.

(Other definitions for by the book that I've seen before include "Strictly following rules" , "According to the rules" .)

I've seen this clue in The Guardian.
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