उपर्यध्यधसः सामीप्ये

Operational rule vidhi

1. उपरि 2. अधि and 3. अधस् are repeated when it expresses uninterrupted nearness.

Word by word (padaccheda)

Target उपर्यध्यधसः ṣaṣṭhī · ekavacanaRight context सामीप्ये saptamī · ekavacana

Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).
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

उपर्यध्यधसः सामीप्ये

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

Commentary

1. उपरि 2. अधि and 3. अधस् are repeated when it expresses uninterrupted nearness.
The word samipya means 'proximity' whether in time or space. As उपर्युपरि दुःखम्, or उपर्युपरि ग्रामम्, अध्यधि ग्रामम्, अधोधो नगरम् ॥ Why do we say 'meaning near'? Observe उपरि चन्द्रमा: ॥ Why the word is not repeated here : उपरि शिरसो घटं धारयति ॥ The relation expressed here is not that of nearness, but that of above and below.

उपर्युपरि पश्यन्तः सर्व एव दरिद्रति ।
अधोधो दर्शने कस्य महिमा नोपजायते ॥

Here the doubling is in the sense of vipsa.

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