<jats:p>There is a peculiar moment in writing a book when something that has existed for years as notes, code, arguments, tracked changes and annoying my unusually patient and kind editors becomes an object with mass. A manuscript can always be revised in one's imagination – a printed book sits on the table, irreversibly typeset, and begins making its own arrangements with the world. About 20lbs of that mass arrived at my doorstep a few moments ago.</jats:p>