Pāṇini sūtras

The substitution of av for avara is optional when astâti follows.

1. vibhāṣāविभाषा

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   vव्	vibhāṣविभाष्	vibhāṣāविभाषा	option	vibhāṣविभाष् + plus āआ

2. avarasyaअवरस्य

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   aअ	avaraअवर	avarasyaअवरस्य	avara [word]	avarअवर् + plus asyaअस्य

Anuvṛtti

1. astātiḥअस्तातिः 5·3·27

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   aअ	astātiअस्ताति	astātiḥअस्तातिः	astātiअस्ताति	astātअस्तात् + plus iḥइः

2. astātiअस्ताति 5·3·40

   Part	Lexeme	Sandhi form	Meaning	Stem + termination
   aअ	astātiअस्ताति	astātiअस्ताति	astātiअस्ताति	astātअस्तात् + plus iइ