The mute of sibilant (jhar) preceded by a consonant and followed by a homogenous mute of sibilant, is optionally elided,
The word हलः is understood. Thus प्रत्त्तम्, अवत्त्तम् have three त, namely, one त substituted for आ by 7.4.47, the second त resulting from the change of द to त by चर्त्व change, the third त is that of the affix. A fourth arises by doubling 8.4.47 of these four, one or two middle ones may be dropped. मरुत्त्त्त here are four तs. A fifth may be added by doubling, and by this rule, one, two or three of them may be elided. मरुत् + दा + क्त = मरुत् + द्त् + त 7.4.47 the word मरुत् being treated as an Upasarga (1.4.59, vartika) = मरुत्त्त्त ॥
Why do we say झरः 'of a jhar'? Compare शार्ङ्गम्, here ङ् which is not a झर् is not elided, though it is followed by a झर् letter. Why do we say झरि 'followed by a jhar'? See प्रियपञ्ञ्चः ॥ This is a Bahuvrihi compound = प्रियाः पञ्चास्य ॥ The word प्रिय stands first in the compound under 2.2.35 (vartika). The full word is प्रियापञ्चन्, the अ is elided by 6.4.134, and we have प्रियपञ्च्न्; and then this न् becomes a palatal ञ् ॥ Here च् is preceded by a हल् letter, and itself is a झर्, and is followed by a homogeneous letter ञ्, but as ञ् is not झर्, the च् is not elided. The elided अ is not considered sthanivat, and so च is considered to be immediately followed by ञ् ॥
Why do we say सवर्णे 'when a homogeneous jhar follows'? Observe तर्प्तु, तर्प्तम् &c, where प् and त् are not homogeneous.
By using the word सवर्णे, the rule of mutual correspondence 1.3.10 is avoided. Had the rule been झरो झरि the rule of mutual correspondence according to order of enumeration would have applied, and the forms शिण्ढि पिण्ढि could not have been evolved by the elision of ड before ढ ॥ For the evolution of these forms see the commentary under 1.1.58. These are the Imperative 2nd Person Singular of शिष् and पिष् ॥ The अ of श्नम् is elided by 6.4.111: the हि is changed to धि by 6.4.101, the ष् is changed to ड् by 8.4.53, the न् of श्नम् is changed to anusvara by 8.3.24; this anusvara is again changed to ण् by 8.4.58; the ध is changed to ढ, and by the present rule, the preceding ड् is elided before this ढ ॥,