Except for the o-stem class, the formation of the IE genitive singular shows a clear and regular development from PIE -os/-es for all noun classes, in Germanic as well as in the other IE languages: Goth. sunaus, gumins, fadrs, nahts; ON sonar, hana, (nom. nǣtt) ; OHG fridō, hanen or hanin, fater, naht; OS suno, gumen; OE suna, guman, fæder, gēs (nom. gōs); Lat. hominis, patris, noctis; Gk. πατρός, κuvóς, etc. The gen. sing. of IE o-stems, however, is attested in forms whose explanation is problematical. This case is built in a number of markedly different ways in the IE languages: for Greek and Indic the indicated ending is the archaic -sjo (e.g. Horn. Gk. ΐπποιo, Skt. asvasya from ); for Illyrian Messapic it is -ihi (e.g. blatθihi ‘Blossii’; cf. the gen. sing, of consonant stems in -as, e.g. platoras); for Latin and Keltic it is -ī (e.g. Lat. servī, Ir. maicc = older maqi from nom. macc 'son'); while in Lithuanian, Lettish, and Slavic, the ablative singular has replaced the genitive (e.g. Lith. diẽvo, Lett. dìeva, Slav, boga 'of God'). In Germanic there is a form that has not yet been satisfactorily accounted for, namely Goth. dagis, ON dags, OE dœges, OS dages, OHG tages, etc. Because the IE languages differ so widely in the form of the gen. sing, of o-stems, most scholars tend to believe that no common proto-form for all the IE languages can be reconstructed.