 I would like to express my gratitude to Jan van Eijck for the enjoyable time of writing the first 2014 version of this article together. Thanks are also due to two anonymous referees for suggesting several improvements and additions for this updated version. Because of Jan’s retirement a few years ago, the 2019 update of the article has been made by me (Rineke Verbrugge) and I therefore bear sole responsibility for any remaining infelicities; please let me know if you spot any.