Watkins (1962)

• Watkins, T. Arwyn. 1962. 'article sur les particules adverbiales', Bulletin of the Board of Celtic Studies XIX, 295-315.

 Fleuriot & Fleuriot (1977:25):
 Arwyn Watkins has done a study of adverbial particles, their morphology and syntax.
 […] to a considerable extent comparative, often mentioning corresponding Brittonic forms.