Praudhamanorama p215

p215

Under 'ato'm' (Pā. Sū. 7.1.24): Under 'svamoḥ': The prescription of am for am is in order to block luk. Under 'am syāt': And this has been explained in deference to the older grammarians, or with the intention that the elision of the conjunct-final consonant applies to a jhal.
In truth, however, the word division (padaccheda) is simply 'm', for the sake of brevity. There, when m is substituted for su, jñānam is established. But in the accusative singular, when m is substituted for the short a by 'ādeḥ parasya' (Pā. Sū. 5.4.54), and the final m is elided by the rule of conjunct-final elision, the desired form is established.
As for what they say—that if this were so, lengthening by 'supi ca' (Pā. Sū. 7.3.102) would take place—that is not so, because of conflict with the metarule of conjunction (sannipātaparibhāṣā). And as for [the claim] that it does not apply in the rule for lengthening, that too is not so, because the application of the metarule of conjunction with respect to the lengthening by 'supi ca' has been hinted at by the Bhāṣyakāra and demonstrated by Kaiyaṭa in the rules 'rudhādibhyaḥ śnam' (Pā. Sū. 3.1.78) and 'śnānnalopaḥ' (Pā. Sū. 6.4.23).
As for what they also say—that atijarasam would not be established—that too is not so; for in the accusative singular, when jaras is substituted by virtue of being subsequent, blocking 'ato'm', the non-application of luk by the metarule of conjunction makes the establishment of the form entirely clear; but in the nominative singular, atijarasam alone is desired, because the substitution of jaras does not apply on account of the metarule of conjunction.