The affix ṭhak comes in the sense of 'it exists' after 1. īpa 2. loma and 3. kūla preceded by anu and prati ; the word being in the Accusative -2nd case in construction.,
The word तद् shows that the words must be in the second case in construction. The verb वर्तते is intransitive, how can it take an object, and how can it be in construction with an objective case? The words in the accusative after the verb वर्तते are not its objects, but are used as adverbs qualifying the sense of the verb, and adverbs are always put in the accusative case. Thus प्रतीपं वर्तते = प्रातीपिकः (प्रतिगता आपोऽस्मिन्, the आ changed to ई 5.4.74 and 6.3.97 retrograde i. e. 'which is unfavourable.' So आन्वीपिकः 'favorable.' प्रतिलोमिकः 'inverse' आनुलोमिकः 'direct.' पातिकूलिकः, आनुकूलिकः The two words प्रातीपिक and आन्वीपिक mean 'unfavourable' and 'favourable' respectively.,