हुझल्भ्यो हेर्धिः

After हु and after a consonant (with the exception of semi-vowels and nasals), धि is substituted for the Imperative affix हि when the latter does not take the augment इट् ।
Thus हु — जुहुधि; झल् consonants; भिद् - भिन्धि, छिन् - छिन्धि ॥ But क्रीणीहि, प्रीणीहि 6.4.113 not ending in consonants. Why 'हि only'? Observe जुहुताम् ॥ Why do we read the anuvritti of हलि into this sutra? When हि does not begin with a consonant, but with a vowel, i.e. when it takes the augment इट्, the rule does not apply. As रुदिहि, स्वपिहि ॥ In the case of जुहुतात्, भिन्तात्, when हि is replaced by तात् 7.1.35 this substitution does not take place because तात् is a later rule in the order of Ashtadhyayi, and because सकृद्गतौ विप्रतिषेधे यद्बाधितं तद्बाधितमेव "When two rules, while they apply simultaneously mutually prohibit each other, that rule of the two which is once superseded by the other, is superseded altogether". When अकच् is added by 5.3.71, धि substitution takes place, as भिन्द्धकि, छिन्द्धकि ॥ The maxim पुनः प्रसङ्ग विज्ञानात् सिद्धम् applies here:- "Occasionally the formation of a particular form is accounted for by the fact that a preceding rule is allowed to apply again, after it had been previously superseded by a subsequent rule."