Аннотация:from the doctoral colloquium of the ETF Leuven; from the helpful advice of Jack Barentsen in the initial stages of my research; from conversations with Christoph Stenschke in Wiedenest, Germany and with John van Eck in the Dutch village of Lexmond; from the reflections of Riemer Faber, during his stay in Kampen in 2016; from participation in the "Lucas-werkplaats" convened by Bart Koet;
