3.4.61 स्वाङ्गे तस्प्रत्यये कृभ्वोः

Word by word (padaccheda)

Right context स्वाङ्गे saptamī · ekavacanaRight context तस्- saptamī · ekavacanaTarget कृ- भ्वोः ṣaṣṭhī · dvivacana

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).

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Full reading

स्वाङ्गे तस्- कृ-भ्वोः

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

Commentary

The affixes क्तवा and णमुल् are added to the roots कृ 'to make' and भू 'to be', in composition with a word denoting a member of one's own body when the affix तस् is joined thereto.
The word स्वाङ्ग has already been defined in sutra 3.4.54. The svanga word in the present case must be such as should end in the affix तस् - a taddhita affix technically called तसि and तसिल् 5.3.78 &c)). Though here there are two roots कृ and भू, and there are two affixes to be applied i. e. क्त्वा and णमुल्; yet the rule of 'respective allocation' 1.3.10 does not apply here. Both the affixes are applied to each of the roots. Thus मुखतः कृत्य गतः or मुखतः कृत्वा गतः or मुखतः कारङ्गतः । Similarly पृष्टतःभूय तिष्ठति or पृष्टतः भूत्वा तिष्ठति or पृष्टतः भावं तिष्ठति ।

Why do we say 'a word denoting a limb of one's own body'? Observe सर्वतः कृत्वा गतः ।

Why do we say 'ending in the affix तस्'? Observe मुखीकृत्य गतः, मुखीभूय गतः ।

Why do we use the word 'the affix'? If तस् is not an affix, but a verb, the rule will not apply. Thus मुखे तस्यति = मुखतः 'throws in the mouth'. With this मुखतः so formed, we cannot apply the rule. Thus मुखतः कृत्वा गतः ।

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