नेर्विशः

After the verb विश् 'to enter', when preceded by the preposition नि, the आत्मनेपद affixes are employed
As विशति 'he enters, but निविशते 'he enters in.'

Even when the augment अट् of the imperfect, Aorist and Conditional tenses intervenes between the root and the preposition, terminations are of the atmanepada. As न्यविशत 'he entered in.'

The नि of the sutra must be an upasarga, because that has a sense, and not any नि. On this there is this paribhasha:-अर्थवद्ग्रहणेनानर्थकस्य "a combination of letters capable of expressing a meaning denotes, whenever it is employed in grammar that combination of letters in so far as it possesses that meaning, but it does not denote the same combination of letters void of a meaning." Thus in मधुनि विशन्ति भ्रमराः 'the beetles enter the honey flowers." Here the नि is a part of the word मधुनि and has no sense by itself, and therefore the verb is in the Parasmaipada and not in the Atmanepada.