 In the imperative/jussive, "tä-" assimilates to the first consonant of the verb root (except when there is no prefix in the affirmative imperative).In the imperfect, "tä-" disappears altogether, though its presence can still be detected from the pattern of vowels and gemination in the verb stem.The first person imperfect and jussive prefix "’ǝ" merges with a following "’a-", and the vowel of the other prefixes ("tǝ", "yǝ", "nǝ") merges with a following "’a-", yielding the vowel "-ä".