Kellens, Jean. 2014. Sur l’origine des Amǝṣ̌as Spǝṇtas. Studia Iranica 43(2). 163-175.
The group of the seven Aməšas Spəṇtas of the Young Avesta is not yet constituted in Old Avesta, but its members are joined together once in each polyhâtic Gāthā as a special phase of the liturgical process by the intervention of certain mediatory entities.