6.1.115 प्रकृत्याऽन्तःपादमव्यपरे

Word by word (padaccheda)

With / by प्रकृत्या tṛtīyā · ekavacanaIndeclinable अन्तःपादम् avyayaRight context अव्यपरे saptamī · ekavacana

With / by Tṛtīyā (3rd case): accompaniment or means.
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").

Full reading

प्रकृत्या अन्तःपादम् अव्यपरे

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

Commentary

The final ए or ओ and the following अ when occurring in the middle half of a foot of a Vedic verse, retain their original forms, except when the अ is followed by ख् or य्।
The word एङः is understood here, but it should be construed here in the nominative case and not in the Ablative. The word प्रकृति means 'original nature, cause'. The word अन्तर् is an Indeclinable, used in the Locative case here and means 'in the middle'. The word पादः 'the foot of a verse' refers to the verses of the Vedas, and not to the verses of secular poetry. The word अति is also understood here. Thus ते अग्ने अश्वमायुञ्जन्; ते अस्मिन् जवमादधुः, उपप्रयन्तो अध्वरम्; शिरो अपश्यम्; सुजाते अश्वसूनृते (Rig. Veda. V. 79.1); अध्वर्यो अद्रिभिः सुतम् (Rig IX. 51.1); शुक्रं ते अन्यत् (Rig. VI.58.1).

Why do we say 'in the inner half of a foot of a verse?' Observe कया मती कुत एतास एतेऽर्चन्ति ॥ Why do we say "when व् or य् does not follow अ?" Observe तेऽवदन् (Rig X. 109.1), तेऽयस्मयम् ॥ Why do we say ए or ओ? Observe अन्वग्निरुषसामग्रमख्यत् ॥ Some read this sutra as नान्तः पादमप्यपरे ॥ According to them, this sutra supersedes the whole rule of juxtaposition or संहिता 6.1.72.

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