न लोकाव्ययनिष्ठाखलर्थतृनाम्

The 6th-Case-affix is not used the express the agent or the object, when the word is governed by an Active Participle ending in the affix ल , or उ , or उक or an indeclinable, or by a Past Participle in the क्त and क्तवतु or by a word ending in an affix having the sense of खल् or by a Noun of agency formed by तृन्।
After these words, the Instrumental case must be employed to denote the Agent, and the Accusative case to denote the object. This sutra debars Genitive which would have come by 2.3.65. The word लोक is formed by ल + उ + उक = ल + ऊक = लोक.

1. The word ल means the substitutes of ल i.e., the Present Participles in शतृ, शानच् 3.2.124, कानच् 3.2.106 क्वसु 3.2.107 कि and किन् 3.2.172. Thus ओदनं पचन्, पचमानः, पेचानः or पेचिवान्, पपिः सोमम्, ददिर्गाः ॥

2. The affix उ is enjoined by 3.2.168, as, कटं चिकीर्षुः, ओदनं बुभुक्षुः ॥ The prohibition applies when a word ending in इष्णुच् 3.2.136 is the governing term, as, कन्यामलंकरिष्णुः ॥

3. The affix उक is ordained by 3.2.154: as आगामुकं वाराणसीं रक्ष आहुः ॥

Vart:- But the word कामुक in the classical Sanskrit, governs the Genitive, as दास्याः कामुकः 'lusting for the slave.'

4. Indeclinables formed by कृत् affixes, as, कटं कृत्वा, ओदनं भुक्त्वा ॥

Vart:- This prohibition, however, does not apply to the indeclinables formed by तोसुन् (III 4.16) and कसुन् 3.4.17, as, पुरा सूर्यस्योदेतोराधेयः पुरा क्रूरस्य विसृपो विरप्शिन् (1.1. 40).

5. Nishtha i.e., क्त and क्तवतु; as ओदनं भुक्तवान् देवदत्तेन कृतम्.

6. The words formed by खलर्थ affixes 3.3.126, as, ईषत्करो भवता कटः, ईषत्पानः सोमो भवता.

7. The तृन् in the aphorism is a pratyahara, formed by taking the तृ of शतृ 3.2.129 and the final न् of तृन् 3.2.135, meaning the affixes जानन् 3.2.128, चानश 3.2.129, शतृ 3.2.130 and तृन् 3.2.135. As सोमं पवमानः, नटमाघ्नानः, अधीयन्, पारायणम्, कर्ता कटान्, वदिता जनापवादान् ।

Vart:- Optionally so, when the root द्विष् takes the affix शतृ, as, चौरं or चौरस्य द्विषन् ॥