Saragih, Ratna, Eduard Hutabarat, Jojor Silalahi, Hendra Putra Purba, and Andar Gunawan Pasaribu. “Pastoral Ecology With Umpasa Cultural Approach In Batak Land”. Migration Letters 21, no. S6 (February 17, 2024): 682–690. Accessed May 19, 2024. https://migrationletters.com/index.php/ml/article/view/7982.