Here is the closing paragraph of the Preface:
It would be impossible for me to conclude this introduction without mentioning one more name—that of Adolf Lindenbaum, a former student and colleague of mine at the University of Warsaw. My close friend and collaborator for many years, he took a very active part in the earlier stages of the research which resulted in the present work, and the few references to his contribution that will be found in the book can hardly convey an adequate idea of the extent of my indebtedness. The wave of organized totalitarian barbarism engulfed this man of unusual intelligence and great talent—as it did millions of others.
Adolf Lindenbaum was killed by the Gestapo in 1941.