ai is placed before the y of nyagrodha instead of vṛddhi when the word stands alone and is not a member of a compound and is followed by a taddhita affix with the indicatory ñ , ṇ or k ,
As नैयग्रोधश्चमसः (= न्यग्रोधस्य विकारः). Why do we say 'when it is alone'? Observe न्यग्रोधमूले भवाः शालयः = न्यग्रोधमूलाः ॥ न्यग्रोध is a derivative word (from न्यग्रोहयति = नीचैर्गतौ परोहैर्वधते), then it would have been governed by 7.3.3, this separate, sutra is then for the sake of making a restrictive rule (niyama) with regard to this word. If it is a primary word, then this sutra makes a Vidhi rule. The word केवल is a jnapaka that the rule of Tadadi applies in this section. See 7.3.8, also.,