In the yajurveda , when an anudātta a is followed by a Guttural or a dha, the antecedent e or o retains it s form, as well as this subsequent a,
Thus अयं सो अग्निः (Yaj. 12. 47), अयं सो अध्वरः ॥ Why do we say when अ is gravely accented ? Observe अधोऽग्रे, here अग्रे has acute accent on the first syllable. Why do we say \when followed by a Guttural (कु) or a ध\? Observe सोऽयमग्निः सहस्त्रियः ॥,