उरत्

Operational rule vidhi

A ऋ letter present in an अभ्यास is converted to अकार.

Word by word (padaccheda)

Target उः ṣaṣṭhī · ekavacanaSubstitute / term अत् prathamā · ekavacana

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

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

Full reading

उः अत्

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)

उः → अत्

Replace uḥ with at. Inherited words (anuvṛtti) may add further conditions.

Commentary

अर् -- उरण् रपरः 1.1.51 is substituted for the ऋ or ॠ of the reduplicate.
As ववृते, ववृधे, शशृधे, नर्नर्त्ति, नरिनर्त्ति, नरीनर्त्ति ॥ The र् is elided by 7.4.60. In the Intensives 7.4.90 &c, are applied, by which after the substitution of अर् by the present sutra, we apply those sutras and add रीक रुक् रिक् &c: for the maxim is अभ्यासविकारेषु अपवादो नोत्सर्गान् विधीन् बाधते "so far as the changes of a reduplicative syllable are concerned special (apavada) rules do not supersede the general (utsarga) rules".

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