Query: Who were Umm Kulthum and Abdel Hafez?
Context: To promote himself and the Liberation Rally, he gave speeches in a cross-country tour, and imposed controls over the country's press by decreeing that all publications had to be approved by the party to prevent "sedition". Both Umm Kulthum and Abdel Halim Hafez, the leading Arab singers of the era, performed songs praising Nasser's nationalism. Others produced plays denigrating his political opponents.