विभाषावरस्य

Operational rule vidhi

The substitution of अव् for अवर is optional when अस्ताति follows.

Word by word (padaccheda)

Substitute / term prathamā · ekavacanaTarget अवरस्य ṣaṣṭhī · ekavacana

Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.
Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).

Dotted words are technical terms. Hover or tap one to see its card.

Full reading

अवरस्य

Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.

As a rewrite rule (sketch from case endings)

अवरस्य → optional

Replace avarasya with vibhāṣā, optionally. Inherited words (anuvṛtti) may add further conditions.

Commentary

The substitution of अव् for अवर is optional when अस्ताति follows.
This declares option when by last it was compulsory. As अवरस्तात् or अवस्तात् वसति आगतः, or रमणीयम् ॥

Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.