-nn, alongside with the inner labialization, is the “light” form used with verbal forms of the suffix conjugation, -yy is the “heavy” form. When the “light” form is to be attached to a verbal form of the prefix conjugation, inner labialization takes place and the final consonant of the base is doubled. The “heavy” suffixes are used with 2 fem. sg, all the plural and impersonal verbal forms, the “light” suffixes are used in all the other cases (Bulakh–Kogan 2013b:105).