Perlindungan hukum bagi pihak ketiga selaku pembeli pada perjanjian jual beli atas tanah bersama milik pasangan suami istri yang telah bercerai : analisis Putusan Mahkamah Agung Republik Indonesia Nomor 2301 K/Pdt/2007 = Legal protection for third parties as the buyer in the land purchase agreement of joint matrimonial property belongs to married couples who have divorced : analysis of a verdict of Supreme Court Republic of Indonesia number 2301 K/Pdt/2007