छन्दस्युभयथा

Operational rule vidhi

In वेदाः, the words भू and सुधी might or might not undergo a यणादेश when followed by an अजादि सुप् प्रत्यय.

Word by word (padaccheda)

Right context छन्दसि saptamī · ekavacanaIndeclinable उभयथा avyaya

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").
Indeclinable An avyaya such as च "and", वा "optionally", न "not".

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

छन्दसि उभयथा

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

Commentary

In the छन्दस् (Vedas), in the case of a अङ्ग (stem) in भू or the word सुधी , are found sometimes the इवङ् and उवङ् and sometimes the semi-vowel substitution.
As विभ्वम्, विभुवम्, सुध्यः and सुधियः; वनेषु चित्रं विभ्वं विशे, विशे विभुवम्, सुध्यो हव्यमग्ने, सुधियो हव्यमग्ने ॥

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