Superb construction, indeed. And once you've figured out the rules of the game it all falls into place quite easily, including the name of the author asked for. This particular playgroup has been a favourite of mine for many years, from the time when I won a civic competition for schoolchildren, by writing a critical essay about it. The prize was a tour of London, Stratford, and Chichester, but my family had already booked a holiday abroad and, to my great regret, I couldn't go. However, the playgroup lives on in my mind.