Комментарий: Labialized vowel in Udi and Tsakh. is secondary (probably due to a contraction *-i + class marker). Mostly used in conjunction with other interrogative stems, like *ʎ:ʷi-š:i,*hi-š:i; but. cf. Tab. erg. ši-li, Ag. Bursh. erg. š:e (nom. u-š:).
See Алексеев 1985,74 (this stem is to be distinguished from another PL interrogative pronoun, *šʷi q.v.).
