Dutch book week
... that during the annual Dutch book week, a book was occasionally published anonymously to let readers guess who the author was?
... that during the annual <b id="mwB-A"><a href="./Boekenweek" id="mwB-E" rel="mw:WikiLink" title="Boekenweek">Dutch book week</a></b>, a book was occasionally published <a href="./Anonymity" id="mwB-I" rel="mw:WikiLink" title="Anonymity">anonymously</a> to let readers guess who the author was?