Grasping the essence

摘要

On March 19, 2010, mathematics lost one of its leading geometric analysts, Johannes Jisse Duistermaat. At age 67 he passed away, after a short illness following a renewed bout of lymphoma the doctors thought they had controlled. `Hans', as Duistermaat was universally known among friends and colleagues, was not only a brilliant research mathematician and inspiring teacher, but also an accomplished chess player, very fond of several physical sports,and a devoted husband and (grand)father. Erik van den Ban and Johan Kolk look back on Duistermaat's life and work in this contribution; it is followed by remembrances and surveys by some of his friends, students, and colleagues.