Questions & Answers about Er þetta afleiðingin einna mistaka?
Why is the plural form einna used here if the translation just says "one" mistake?
Why are einna and mistaka in the genitive case?
They are in the genitive case to show possession or origin, which translates into English as "of one mistake". In Icelandic, you often express "of [noun]" by placing that noun in the genitive case directly after the main noun (afleiðingin).
The dictionary form is mistök. Why does the vowel change to an 'a' in mistaka?