Протонахский: *=u / =a
Значение: to be, is (an auxiliary verb)
Чеченский: =u
Ингушский: =a
Бацбийский: =a
Комментарии: The auxiliary verb "to be", used only in the present tense. The -u-vocalism in Chech. is probably secondary (*u_-i > *w-u in the first class, whereas *-i > -a in other classes).
