As Greece Heads for Default, Voters Prepare to Vote in Pivotal Referendum on More Austerity; Historic Iran Nuclear Deal Hangs in the Balance as Talks Enter Final Round; Egypt’s Power Struggle Intensifies with Killing of Prosecutor Behind Mass Jailings of Islamists; Amid Warnings of Famine, Yemeni Civilians Trapped Inside Conflict with No End in Sight; The Centenary of a Revolutionary: Legendary Activist, Organizer Grace Lee Boggs Turns 100.