20809 contract law/ authenticated documents contract law Federal supreme court of Ethiopia cassation decisions volume 5 በባለስልጣን ፊት በተረጋገጡ ሰነዶች ላይ ያሉትን ፊርማዎችና የሰነዶቹን ይዘት ማስተባበል ስላለመቻሉ Cassation Decision no. 20809