tonight an historic agreement with wufb america's staunchest'd ver sierras. iranian leaders agreeing to give unprecedented access to international nuclear weapons inspectors. in exchange for easing economic sanctions against the isolated country. if iran cheats says president obama, the world will know about it. how's the plan being received? for the moment with a lot of celebrating. it's abc's chief foreign correspondent terry moran. >> reporter: good evening, juju. the deadlines came and went here. the negotiators, some of them came and went. but those who stuck it out emerged after several marathon sessions to announce a breakthrough. in the words of secretary of state kerry, they have opened a window of possibility for a deal that is hoped will bring iran's nuclear ambitions under strict international control. on the streets of tehran tonight, there was joy. to so many of the people of iran, so long cut off from the world economy, this deal is about more than nuclear technology and international relations, it's about hope. in luzon, switzerland, where neg