"This historical thicket is rendered all but impenetrable by the facts that, as Browning lucidly and vividly demonstrates, German anti-Semitism was hardly a fixed concept but, rather, evolved and mutated with the ever shifting circumstances; that the Nazi regime and its chains of command and decision were highly decentralized — which meant that at any given moment the interpretations and conceptions of, say, Goebbels and Rosenberg concerning the timing and realization of the Final Solution could vary significantly from those of Himmler and Heydrich; and, most important, that the documentary evidence is both vast and frustratingly incomplete."