When your enemy is sworn to exterminate every one of you, can you -- should you -- try to cut a deal with him to at least save some lives knowing that others are doomed?
The question lies at the heart of a new documentary by Claude Lanzmann, author of "Shoah," the hugely-acclaimed tableau of the Holocaust.
"The Last of the Unjust," premiering at Cannes on Sunday, explores a moral dilemma that Lanzmann briefly touches on his 1985 masterpiece.
For three and a half hours, the viewer is taken through an exploration of Benjamin Murmelstein, the last president of the Jewish Council in the "model ghetto" of Theresienstadt in Nazi-annexed Czechoslovakia.
Set up by SS colonel Adolf Eichmann as a bogus town run by Jews themselves -- a Potemkin village designed to dupe the world -- Theresienstadt was one of the grimmest chapters in the long record of Nazi atrocities.
It housed 50,000 Jews at its peak periods. Over four years, more than 150,000 inhabitants were killed, many of them shipped to the gas chambers of Auschwitz.
"It was the peak of Nazi cruelty and perversity... a unique combination of lies and naked violence," Lanzmann, 87, said in an interview with AFP in February.
To run Theresienstadt, the Nazis formed a Jewish Council, comprising 12 members and a leader, "the Elder of the Jews," or Judenaeltester in German. Those who refused the appointment were killed.
The first Elder was sent to Auschwitz in 1943 and killed six months later; the second was executed in Theresienstadt in 1944.
The documentary describes the extraordinary and controversial tale of Benjamin Murmelstein, a former Grand Rabbi of Vienna who became the third and final Elder in Theresienstadt and the only one in all of eastern Europe to survive the war.
Survival meant that he became a target. In the early 1960s, Murmelstein was bitterly attacked by some Holocaust survivors, who accused him of collaboration. There were even calls for him to be hanged, like Eichmann, whom Murmelstein knew intimately from Vienna.
The documentary is based on hours of filmed interviews that Lanzmann had with Murmelstein in 1975, 14 years before his death.
In it, Murmelstein comes across as hugely compelling, a man fiercely intelligent, courageous and ironic, harsh with others but also with himself.
Every day, he faced demands from the Nazis that he was obliged to comply with -- but he did his utmost to delay or subvert them, and in the process enabled some to avoid the death marches ordered by Hitler, yet knowing that others were doomed.
He is far from being a stooge or power-mesmerised monster, as other Elders in the eastern European ghettos were and as he himself was later portrayed.
"By taking huge risks (in Vienna), he managed to get 120,000 Austrian Jews out of the clutches of their persecutors, and what he recounts is a magisterial lesson in history," said Lanzmann.
"(...) One of the lessons of 'The Last of the Unjust,' in my view, is that at a certain point you no longer have any other choice than to comply and obey, that all resistance becomes impossible.
"That said, Benjamin Murmelstein fought tirelessly right to the end against the killers. As he said, the Nazis wanted to make him into a puppet, but the puppet had learned to pull the strings."
As the holder of a diplomatic passport issued by the Red Cross, Murmelstein could have fled abroad after the war.
Instead, he voluntarily put himself forward for arrest by the Czechoslovak authorities after a number of Jews accused him of collaborating with the enemy.
He spent 18 months in prison before being acquitted of all charges. He went into exile in Rome, where he found life tough, but he never went to Israel.
Murmelstein's recollections, said Lanzmann, are doubly precious, as they prompt a new interpretation of Eichmann, who was kidnapped by Mossad agents in Argentina and hauled to Israel for trial, culminating in his execution in 1962.
German philosopher Hannah Arendt, in her account of the trial, described Eichmann as the stereotypical bureaucrat, embodying "the banality of evil".
But Murmelstein portrays Eichmann as a "demon," fanatical in his anti-Semitism, violent and corrupt.