According to the opinion of śākalya , the simple vowels with the exception of a , when followed by a non-homogenous vowel, retain their original forms; and if the vowel is long, it is shortened.,
Thus दधि अत्र, मधु अत्र, कुमारि अत्र, किशोरि अत्र ॥ In the alternative we have दध्यत्र, मध्वत्र, कुमार्यत्र, किशोर्यत्र ॥ Why do we say 'the इक् vowels i.e. simple vowels with the exception of अ'? Observe खट्वेन्द्रः ॥ Why do we say 'followed by a non-homogenous vowel'? Observe कुमारीन्द्रः ॥ The name of Sakalya is mentioned for the sake of respect. Because the alternative nature of this sutra is clear from its very formation.
Vart:- This rule of Sakalya is prohibited in the case of words formed by an affix having an indicatory स् and of words which form invariable compounds (nitya samasa):- Thus अयं ते योनिर्ऋत्वियः, प्रज्ञां विदाम ऋत्वियाम् The word ऋत्विय is formed by a सित् affix, namely by घस् 5.1.106, added to ऋतु; and therefore the उ is changed to व ॥ Before a सित् affix the previous word is considered a pada 1.4.16 Of nitya-compounds are वैयाकरणः, सौवश्वः, व्याकरणं, कुमार्यर्थम् which are so by 2.2.18 &c.
Vart:- In the Vedas ईषा अक्षः &c are found uncombined. As, इषा अक्षा, का ईमिरे पिशंगिला, यथा अङ्गदः, पथा अगमन् &c.,