वा पदान्तस्य

Operational rule vidhi

An अनुस्वार occurring at end of a पद when followed by a यय् वर्ण is optionally converted to the परसवर्ण.

Word by word (padaccheda)

Indeclinable वा avyayaTarget पदान्तस्य ṣaṣṭhī · ekavacana

Indeclinable An avyaya such as च "and", वा "optionally", न "not".
Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).

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

वा पदान्तस्य

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

Commentary

In the room of अनुस्वारा, final in a पद, the substitution of a letter homogenous with the latter is optional.
Thus तं कथं चित्रपक्षं डयमानं नभःस्थं पुरुषोऽवधीत् or तङ्कथञ्चित्रपक्षण्डयमानन्नभः स्थम्पुरुषोऽवधीत् ॥

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