Utomo, A. B., and F. . Widiana. “Green Sister City Cooperation of Surabaya and Kitakyushu: Beyond Ceremonial Paradiplomacy”. Thammasat Review, vol. 27, no. 2, Dec. 2024, pp. 316-34, https://sc01.tci-thaijo.org/index.php/tureview/article/view/240960.