जश्शसोः शिः

Operational rule vidhi

The जस्/शस्-प्रत्ययs that follow a नपुंसकलिङ्ग word get 'शि' आदेश.

Word by word (padaccheda)

Target जश्- शसोः ṣaṣṭhī · dvivacanaSubstitute / term शिः 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

जश्-शसोः शिः

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)

जश्- शसोः → शिः

Replace jaś-śasoḥ with śiḥ. Inherited words (anuvṛtti) may add further conditions.

Commentary

After a neutral अङ्ग (stem), इ is substituted for the endings (जस् and शस्) of Nominative 1st-Case and Accusative -2nd case.
Thus कुण्डानि तिष्ठन्ति, कुण्डानि पश्य, दधिनी, मधूनि, त्रपूणि, जतूनि ॥ The augment न् is by 7.1.72. The word शस् in the sutra being read along with जस् denotes the Accusative Plural ending शस् and not the Taddhita affix शस् 5.4.43; as कुण्डशो ददाति, वनशः प्रविशति ॥

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