According to the opinion of āpiśali, the vṛddhi is optionally the single substitute, when the a or ā of a preposition is followed by a Denominative Verb beginning with ṛ,
Thus उपार्षभीयति or उपर्षभीयति, उपल्कारीयति or उपाल्कारीयति ॥ The ऋ and लृ are considered as homogenous letters, therefore the word ऋ in the last sutra includes लृ also. The name of the Grammarian Apisali is mentioned for the sake of respect; the वा itself was enough to make it an optional rule.,