वा सुप्यापिशलेः

Operational rule vidhi

When an अवर्णान्त उपसर्ग is followed by a ऋकारादि सुब्धातु, both of them are optionally replaced by a single वृद्धि letter.

Word by word (padaccheda)

Indeclinable वा avyayaRight context saptamī · ekavacanaTarget आपिशलेः ṣaṣṭhī · ekavacana

Indeclinable An avyaya such as च "and", वा "optionally", न "not".
Right context Saptamī (7th case): "when X follows", the operation applies to what precedes (1.1.66 तस्मिन्निति निर्दिष्टे पूर्वस्य). Also a condition or domain ("in the sense of").
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 आपिशलेः

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

Commentary

According to the opinion of आपिशलि, the वृद्धि is optionally the single substitute, when the अ or आ of a preposition is followed by a Denominative Verb beginning with ऋ।
Thus उपार्षभीयति or उपर्षभीयति, उपल्कारीयति or उपाल्कारीयति ॥ The ऋ and लृ are considered as homogenous letters, therefore the word ऋ in the last sutra includes लृ also. The name of the Grammarian Apisali is mentioned for the sake of respect; the वा itself was enough to make it an optional rule.

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