 Bridges thanks Philip Catton for kindly advising him about an early version of this entry; Fred Richman, the late Ray Mines, Bill Julian, Hajime Ishihara, Helmut Schwichtenberg, and Peter Schuster, for decades of friendship, mathematical collaboration, and support during visits to their institutions; Luminita Vîţă, Hannes Diener, Matt Hendtlass, Maarten McKubre-Jordens, Josef Berger, Iris Loeb, and many other students, postdocs, and colleagues, for their participation in the constructive programme; the University of Buckingham, England, for giving him opportunity and encouragement at the start of his academic career; and the Universities of Waikato and Canterbury, for supporting him in New Zealand since 1989. Last, but not least, he thanks Hajime Ishihara for stepping into the authorial breach made by the untimely death of Erik Palmgren.