The substitution of av and āv for o and au also takes place before an affix beginning with ya,
The वान्त are those which end in व् viz. अव् and आव् ॥ Of the four substitutes taught in the preceding sutra, those which end in व् (viz. अव् and आव्) also come when an affix with an initial य follows. It follows that the substituted letters must be ओ and औ ॥ Thus बभ्रु + यञ् = बाभ्रो + य = बाभ्रव्यः 6.4.146 and (IV. I. I05). So also माण्डव्यः, शंकव्यंदारु, पिचव्यः कार्पासः, नाव्यो 4.4.91 हृदः ॥ Why do we say \अव् and आव्\? Observe रायमिच्छति = रैयति, no change of ऐ before य ॥ Why do we say \before य\? Observe गोभ्याम्, नौभ्याम् ॥ Why do we say \an affix\? Observe गोयानम्, नौयानम् ॥
Vart:- The word गो is changed before यूति in the Vedas. As गो + यूति = गव्यूति, as आनो मित्रा वरुणा घृतैर्गव्यूतिमुक्षतम् ॥ Why do we say in the Vedas? Observe गोयूतिः ॥
Vart:- This substitution takes place when referring to the measure of a road:- as, गव्यूति मात्रमध्वानं गतः ॥ This is in the secular literature, गव्यूति meaning क्रोशयुगम् ॥,