For the vowel of the roots 1. āp 2. jñapi and 3. ṛdh there is substituted long ī before san of the Desiderative when it begins with s,
Thus आप्-ईप्सति, ज्ञपि-ज्ञीप्सति, ऋध्-ईर्त्सति 1.1.51. The reduplication is dropped by 7.4.58. In the Causative stem ज्ञपि there are two vowels, the इ (णि) is dropped by purva-vipratishedha (the prior debarring the subsequent) according to 6.4.51, and ई (substituted for अ according to the present sutra. The word सन् is to be read into the sutra, otherwise प्रापस्यति ॥ The सन् must begin with स् i.e should not take the इट् augment, as in जिज्ञपयिषति, अर्हिधिषति ॥ The roots ज्ञपि and ऋध् are optionally सेट् in the Desiderative by 7.2.49.,