Words and Proper Names

an (article)

2657.
de Bernardo Stempel (Patrizia): Indogermanische Demonstrativa und der altirische Artikel.
In ZCP 41 (1986), pp. 259–271.
Traces the development of the Old Irish article from its origin in the Indo-European demonstrative stem *so/to- to its partial substitution by the root *sem- ‘one’.