Former Soviet Union leader Mikhail Gorbachev, former Polish President Lech Walesa, former President of South Africa Frederik W. de Klerk and Kathrada Ahmed, a South African politician representing Nelson Mandela, from right, participate in the 10th World Summit of Nobel Peace Laureates in Berlin, Germany, Tuesday, Nov. 10, 2009. Due to the 20th anniversary of the fall of the Berlin Wall, the two-day-summit takes place in the German capital.