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Planter and peasant : colonial policy and the agrarian struggle in East Sumatra 1863 - 1947
Pelzer, Karl J., (1978)
Subsistence- and commodity production in the Simalungun highlands of North Sumatra
Clauss, Wolfgang, (1981)
Industri besar dan sedang di Sumatera Utara - Large and medium manufacturing establishments in North Sumatera
(1978)