Oh, OK, sure. It sounds like the Szilard petition wanted to incentivize Japan to surrender by conceding to them some post-war self-determination. The US would not accept this -- which, I as I said, might have been immoral -- so, to me, the ambiguity of the surrender terms in the Potsdam Declaration is not really surprising or damning. If we can trust Wikipedia, Japan declined surrender even after the first bomb on Hiroshima in the hopes of striking better terms with the USSR.

For others, here are the relevant excerpts from the Szilard petition, which is quite short and worth reading in full:

> We feel, however, that such attacks on Japan could not be justified, at least not unless the terms which will be imposed after the war on Japan were made public in detail and Japan were given an opportunity to surrender....If such public announcement gave assurance to the Japanese that they could look forward to a life devoted to peaceful pursuits in their homeland and if Japan still refused to surrender our nation might then, in certain circumstances, find itself forced to resort to the use of atomic bombs....we, the undersigned, respectfully petition: first, that you exercise your power as Commander-in-Chief, to rule that the United States shall not resort to the use of atomic bombs in this war unless the terms which will be imposed upon Japan have been made public in detail and Japan knowing these terms has refused to surrender; ...

http://www.dannen.com/decision/45-07-17.html