इट् सनि वा

The Desiderative स् may optionally take इट् (which is optionally lengthened also) after the said after वृ and ॠ ending roots.
As वुवूर्षति । विवरिषते । विवरीषते । प्रावुवूर्षति । प्राविवरिषति । प्राविवरीषति । ॠकारान्तेभ्यः । तितीर्षति । तितरिषति । तितरीषति । आसिस्तीर्षति । This Parasmaipada form is not valid, according to Padamanjari. आतिस्तरिषति । आतिस्तरीषति । सनि ग्रहगुहश्चेत इट्प्रतिषेधे प्राप्ते पक्षे इडागमो विधीयते । इटश्च वॄतो वेति पक्षेदीर्घः । चिकीर्षति जिहीर्षति इत्यत्रोपदेशोधिकाराल्लाक्षणिकत्वाच्च इडागमो न भवति ॥

The इट् was prohibited by 7.2.12, in case of the Desideratives, hence this sutra : when इट् is added, it may be lengthened by 7.2.38. The augment इट् however is not added in चिकीर्षति and जिहीर्षति, as they are formed from कृ 'to do' and हृ 'to lose', which do not take इट् at all. Because here, though the short ऋ is lengthened before सम्, by 6.4.16, yet such lengthening will not make the roots long ॠ ending roots. Because the anuvritti of the word upadesa is understood here from 7.2.10, so that the rule applies to those roots only which in upadesa' or Dhatupatha end in long ॠ and not those whose ॠ is lengthened by some Grammatical rule. Moreover, the long ॠ in कृ and हृ is temporary only, as it is replaced by long ई ॥ (See 6.4.16, for lengthening). The Desiderative of कॄ - चिकरिषति, however, does not lengthen its vowel 7.2.75.