http://publikasi.umy.ac.id/files/journals//15/articles/1558/public/1558-4801-1-PB.pdf
http://publikasi.umy.ac.id/files/journals//15/articles/733/public/733-1521-1-PB.pdf
http://publikasi.umy.ac.id/files/journals//15/articles/3172/submission/review/3172-3335-1-RV.docx
http://publikasi.umy.ac.id/files/journals//15/articles/3172/submission/original/3172-3305-1-SM.docx
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