Praudhamanorama p117

p117

[On] atrānunāsikaḥ pūrvasya tu vā (Pā. sū. 8.3.2): There is a dichotomy as to whether this is a governing rule (adhikāra) or an operative rule (vidhi). On the first view, the mention of "atra" is useless, because the section on ru is obtained merely from the governing rule. But on the view that it is a governing rule, the word "tu" is for the sake of showing a distinction from the subsequent element undergoing the operation—namely, that for the subsequent element ru is obligatory, but for the prior element nasalization is optional; on the operative-rule view, it is purposeless. The mention of "vā" is for clarity, because it is established merely from the inferential indicator (jñāpaka) "anunāsikātparaḥ—" (Pā. sū. 8.3.4); for without an option, the alternative of absence of nasalization is not possible. To convey this very point, the two words "tu" and "vā" were not stated in the gloss.