Of a root ending in r or v , the penultimate i or u is lengthened before a consonantal beginning affix.,
Thus आस्तीर्णम्, विस्तीर्णम्, विशीर्णम्, अवगूर्णम्, all ending in र् ॥ So also, दीव्यति, सीव्यति ending in व् ॥
The phrase \of the root\, is understood here also. Therefore not here, दिव्यति and चतुर्यति, which are derived from the nouns दिव and चतुर i.e. दिवमिच्छति = दिव्यति, and चतुर इच्छति = चतुर्यति ॥
The phrase इकः \of the vowels इ or उ\ is understood here also. Therefore not here, स्मर्यते, भव्यम् ॥
This rule applies to cases which are not final in a pada: but to cases where र् or व् are in the middle of a pada or word.,