i is substituted for the final u or ū of a reduplicate before a labial, a semi-vowel and before j when a or ā follows these consonants, in the Desiderative.,
The word पु-यण्-जि is the Locative singular of the samahara dvandva compound of those three words-पु, यण् and ज् ॥ The samasanta affix टच् 5.4.106 does not come, as these affixes are anitya. The word अ-परे means that after which is the letter अ ॥
Thus: 1. Labial:- पिपविषते, पिपावयिषति, विभावयिषति; 2. Semi-vowel:- यियविषति, यियावयिषति, रिरावयिषति, लिलावयिषति; 3. ज-जिजावयिषति from the root जु ॥
The word पिपविषते is from पू, which gets इट् augment in सन् 7.2.74, then there is guna, and अत् substitutions, but these latter being sthanivat for reduplication 1.1.59, पू is doubled: and for ऊ there is substituted इ by the present sutra. पिपावयिषति is the Desiderative of the Causative of पू ॥ विभावयिषति is the Desiderative of the Causative of भू ॥ यियविषति is the Desiderative of यु 'to mix', which is सेट् by 7.2.49. यियावयिषति is the Desiderative of the Causative of this root. The words रिरावयिषति and लिलावयिषति are the Desiderative of the Causatives of रौति and लुनाति ॥
This sutra indicates the existence of the following maxim:- अद्विर्वचन निमित्तेऽपि स्थानिवद् भवति, \though not the cause of reduplication, the substitute which takes place when णि follows, becomes like the original\. Thus in विभावयिषति we have भावि + सन् from भू + णि + सन्, here the आद् substitute caused by णि is sthanivat to ऊ, otherwise there would be no उ in the reduplicate to be operated upon by the present sutra. See 6.1.31 also. Why do we say \for the उ or ऊ\? Observe पापच्यते, the Desiderative of which will be पापचिषति ॥ Why do we say \followed by a labial, semi-vowel or ज\? Observe अव नुनावयिषति, according to Padamanjari it is अव तुता वयिषति from the sautra root तु ॥ जुहावयिषति ॥ Why do we say 'when these consonants are followed by an अ'? Observe बुभूषति ॥,