Seven southern European leaders are holding a summit to emphasize their commitment to the European Union, in the wake of Britain’s vote to leave the bloc. The informal half-day meeting in Lisbon on Saturday includes the leaders of France, Italy, Spain, Greece, Cyprus and Malta, as well as host Portugal. Portuguese officials say the seven leaders will commit their countries to closer cooperation on border security and efforts to fight terrorism. They will also consider ways of spurring economic growth and coordinating their economies, which all use the euro currency. EU growth is on the whole sluggish. The countries have already signaled they are prepared to surrender more national sovereignty to EU institutions.