The cerebral sound is optionally substituted for the dh of ṣīdhvam and of the Aorist and the liṭ (Perfect Tense) after the augment iṭ when the stem ends in inn,
Thus लू + इट् + षीध्वम् = लविषीध्वम् or लविषीढ्वम् so also पविषीध्वम् or पविषीढ्वम् fromपू ॥ Aorist:- अलविध्वम् or अलविढ्वम् ॥ Perfect:- लुलुविध्वे or लुलुविढ्वे ॥
The word इण is understood here and it qualifies the word इट्, so that the stem should end in an इण् vowel which should be followed by the इट् augment and this letter should be followed by षीध्वम् and the ध beginning affixes of the Aorist and the Perfect. If the stem does not end in an इण् vowel, the rule will not apply; as आसिषीध्वम् from the root आस उपवेशने ॥
Then in the word उपदिदीयिद्ध्वे, will the cerebral change not take place by the option of this sutra or otherwise? This is from the root दीङ् क्षये in the Perfect with the augment इट् (VII. 2. 13.), and युट् (by VI. 4. 63). Some say that as the augment युट् intervenes between the stem ending in ई (इण् vowel), and the augment इट्, therefore this rule will not apply and there will not be the optional ढ ॥ Others hold that the anuvritti of अङ्गात् has ceased, and the anuvritti of इण् is only current, in this sutra, and there is no intervention and so there will be the optional change into ढ ॥,