Suwandi, Suwandi, and Kuwat Subyantoro. “Review on the Opinions about the Aplication of Diminishing Returns Law”. International Journal of Sciences: Basic and Applied Research (IJSBAR), vol. 29, no. 1, Aug. 2016, pp. 155-63, https://www.gssrr.org/JournalOfBasicAndApplied/article/view/6104.