Korean revolutionary opera, derived from traditional Korean operas, known as ch'angguk, often utilize variations on Korean folk songs. Old fairy tales have also been transformed to include revolutionary themes. As part of the party's policy of preserving the best from Korea's past, moreover, premodern vernacular works such as the Sasong kibong (Encounter of Four Persons) and the Ssangch'on kibong (Encounter at the Two Rivers) have been reprinted.