Before a taddhita affix with an indicatory ñ , ṇ or k the vṛddhi is not substituted for the first vowel after y or v but ai and au are respectively placed before the semi-vowels in dvāra etc.,
As द्वारे नियुक्तः = दौवारिकः, दौवारपालम् from द्वारपाल ॥ The Tadadi rule applies here. सौवरः from स्वर, (स्वरमधिकृत्य कृतो ग्रन्थः) ॥ So also सौवरोऽध्यायः, सौवर्थः सप्तम्यः ॥ वैयल्कशः from व्यल्कश, (व्यल्कशे भवः) सौवस्तिकः from स्वस्ति, (स्वस्तीति आह) सौवः from स्वर् (स्वर्भवः) ॥
Vart:- The last vowel, with the consonant, if any, which follows it, is elided in the Indeclinables : as सौवर्गमिकः (= स्वर्गमनमाह) ॥
Some read the word स्वाध्याय also in this list, but it is unnecessary, as it would be governed by the last rule, because it is a compound of सु + अध्याय (शोभनोऽध्याय), or it may be a compound of स्व + अध्याय, then also it is unnecessary, as स्व is separately mentioned, in this list, and therefore when स्व begins a word it would get this peculiar substitution then also. Similarly स्फैयकृतः from स्फ्यकृत; सौवादुमृदुम् from स्वादुमृदु, शौवनम् from श्वन् the prakriti-bhava is by 6.4.167 while शौवम् from श्वन् where there is no prakritibhava (by अञ् 4.3.154): शौवादंष्ट्रः (श्वादंष्ट्र्यां भवः). Similarly सौवम् from स्व (= स्वस्येदं); सौवग्रामिकः from स्वग्राम with the affix ठञ् (अध्यात्मदित्वाट् ठञ्). This sutra is made because the य् and व् here are not finals of a पद or word, as they were in the preceding sutra. The following is a list of Dvaradi words.
1 द्वार, 2 स्वर, 3 स्वाध्याय, 4 व्यल्कश, 5 स्वस्ति, 6 स्वर् (स्वर), 7 स्फ्यकृत, 8 स्वादुमृदु, 9 श्वस्, 10 श्वन्, 11 स्व ॥,