अन्तिकबाढयोर्नेदसाधौ

Operational rule vidhi

For अन्तिक is substituted नेद and for बाढ is साध when the affixes इष्ठन् and इयसुन् follow.

Word by word (padaccheda)

Target अन्तिक- बाढयोः ṣaṣṭhī · dvivacanaSubstitute / term नेद- साधौ prathamā · dvivacana

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, dashed ones pratyāhāras (names for classes of sounds or affixes). Hover or tap one to see its card.

Full reading

अन्तिक-बाढयोः नेद-साधौ

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)

अन्तिक- बाढयोः → नेद- साधौ

Replace antika-bāḍhayoḥ with neda-sādhau. Inherited words (anuvṛtti) may add further conditions.

Commentary

For अन्तिक is substituted नेद and for बाढ is साध when the affixes इष्ठन् and इयसुन् follow.
Thus नेदिष्ठम्, नेदीयः, साधिष्ठः and साधीयान् ॥ सर्वाणीमान्यन्तिकानि इदमेषामतिशयेन, नेदिष्टम् । उभे इमे अन्तिके इदमनयोरतिशयेन नेदीयः । इदमस्मान्नेदीयः । सर्वइमे बाढमधीयते । अयमस्मात्साधीयोधीते ॥

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