COMMENT: The verb demonstrates an old Ablaut *-ä̆sA (reflected in PN *-is-, PWC *sǝ- and probably also Ud. ars-) / *-os(w)V (reflected in PA *-us-, PL *ʔos:V-). It is interesting that the grade *-ĭsV is not attested. Correspondences are regular.
Cf. also HU: Hurr. aš:- 'to sit', Urart. aš- 'to sit' (caus. 'to put'), see Diakonoff-Starostin 1986, 37.