Pāṇini sūtras

ā is substituted for the final of yuṣmad and asmad before a case-ending, beginning with a consonant, when it is not a substitute.

1. yuṣmad+asmadoḥयुष्मद्+अस्मदोः

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   yय्	yuṣmadयुष्मद्	yuṣmadयुष्मद्	yuṣmad [word]युष्मद् [wओर्द्]	yuṣmadयुष्मद्
   aअ	asmadअस्मद्	asmadoḥअस्मदोः	asmadअस्मद्	asmadअस्मद् + plus oḥओः

2. an+ādeśeअन्+आदेशे

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   aअ	naन	anअन्	not	naन
   āआ	ādeśaआदेश	ādeśeआदेशे	substitute	ādeśआदेश् + plus eए

Anuvṛtti

1. vibhaktauविभक्तौ 7·2·84

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   vव्	vibhaktiविभक्ति	vibhaktauविभक्तौ	declension	vibhaktविभक्त् + plus auऔ