Keabsahan surat kuasa jual mengenai jual beli tanah : studi kasus putusan Mahkamah Agung Republik Indonesia Nomor : 01./PDT.G/2011/PN KSP tanggal 19 Agustus 2011 = Power of attorney to sell validity of the sale and purchase of land : case study verdict of Indonesia Supreme Court number 261/PDT.G/2011/PN.KSP date August 19, 2011