BERLIN — Germany's four living former presidents have jointly urged Iran to release two journalists detained in October in connection with a highly publicized stoning case.Sunday newspaper Bild am Sonntag, for whom the journalists were working in Iran, carried the rare joint appeal of the country's elder statesmen Horst Koehler, Roman Herzog, Richard von Weizsaecker and Walter Scheel.Koehler was quoted as saying the Iranians should free the journalists before Christmas in a gesture of humanity.Herzog also urged their release and was quoted as saying, "the idea of mercy plays an important role in the Koran."The two journalists were arrested while interviewing the son and lawyer of 43-year-old Sakineh Mohammadi Ashtiani, who was sentenced to death by stoning for adultery.