उस्य् अपदान्तात्

The आत् is understood here. This debars the guna substitution taught in (VI. I. 87). Thus भिन्द्या + उस् = भिन्द्युः, छिन्द्या + उस् = छिन्द्युः ॥ अदा + उस् = अयुः, (लुङ् of दा) अया + उस् = अयुः ॥ All these are examples of लिङ् (Potential) and लङ् (Imperfect). Thus भिन्द् + यासुट् + झि (the यासुट् is added by 3.4.103) = भिन्द् + य + उस् (जुस् replaced झि 3.4.108) = भिन्द्युस् ॥ अदा + सिच् + झि = अदा + o 2.4.77 + जुस् 3.4.10 = अदा + उस् = अदुः ॥ अ + या + झि = अ + या + उस् 6.4.111 = अयुः ॥ The उस् is also the substitute of झि in लिट् (Perfect) see 3.4.82. When the preceding vowel is not अ or आ, this rule does not apply. Thus the 3rd person plural of the Perfect of कृ is:- चकृ + उस् = चक्रुः ॥ So also from भी we have अबिभे + उस् = अबिभयुः ॥ The word अपदान्तात् 'not being final in a pada' does strictly speaking, serve no good purpose in this sutra. For the affix उस् can never be added to a Pada, it must always be added to a stem, that has not yet risen to the rank of a Pada. If उस्, however, be taken as the syllable उस् (whether an affix or part of an affix or not), then the limitation of अपदान्तात् becomes valid. Thus का + उस्रा = कोस्रा, का + उषिता = कोषिता ॥ Most likely this word has been read here for the sake of the subsequent sutra or because उस् syllable is taken here and not merely the affix उस् ॥,