Par­tial fund­ing for this volume was gen­er­ously provided by the fol­low­ing in­sti­tu­tions: the pro­ject Lipschitz Geo­metry of Sin­gu­lar­it­ies (LISA ANR-17-CE40-0023) of the Agence Na­tionale de la Recher­che (France); and Barn­ard Col­lege (New York), via a re­search grant to math­em­atician Dusa Mc­Duff, who used part of her grant to high­light the re­search ef­forts of Wal­ter Neu­mann, a dis­tin­guished mem­ber of the Barn­ard Math­em­at­ics De­part­ment.