सूददीपदीक्षश्च

The affix युच् does not come after the verbs सूद् 'to strike', दीप् 'to shine' and दीक्ष् 'to initiate'.
These three verbs are anudattet, and by sutra 3.2.149, would have taken युच्. The present sutra prohibits that. Therefore they take तृन्. As, सूदितृ Ist. sing सूदिता 'one who strikes'; दीपितृ 'one who shines'; दीक्षितृ 'one who initiates'.

Now, it might be objected-- "We find that sutra 3.2.167 specifically enjoins the affix र after दीप्; this apavada rule will therefore, supersede the general rule; where is then the necessity of the present rule? If you say that the affix युच् is also obtained by the rule of non-uniformity 3.1.94, we reply that the Paribhasha given under sutra 146 and 150 will prevent that." This objection is answered by saying that the above-mentioned Paribhasha is not of universal application; there are exceptions to it, as कम्रा युवतिः and क्रमना युवतिः 'a young girl' which are both valid forms derived by adding र and युच् to the verb कम्. So also कम्प्रा and कम्पना शाखा 'a shaking branch'.

If we prohibit युच् after the root सूद, how do we get the forms मधुसूदन and रिपुसूदन ? This objection may be answered in three ways: (1) the present is an anitya rule, not of universal application, which can be inferred from finding this sutra separated from the last (yogavibhaga), when it was easier to make them one, (2) the words मधुसूदन &c belong to the मन्दादि class 3.1.134 taking the affix ल्यु or (3) they are formed by 3.3.113 by the affix ल्युट्.