Whether you bang out Friday puzzles and know a four-letter toiletry product is (almost) always “ATRA” or mull over Sunday puzzles for days, you'll dig the clue-by-clue musings of this blog. Outed last year as SUNY Binghamton professor Michael Sharp, “Rex” knows all the puzzle writers by reputation, and takes delight in clever cluing. Will Shortz is a regular reader, maybe because Rex always admits when a puzzle is needlessly thorny or a clue too obscure (see his “Natick Principle”).