नामन्यतरस्याम्

After an oxytoned stem which ends in a light vowel, the genitive ending नाम् has optionally the acute accent.
Thus अग्नी॒ना꣡म् or अग्नी꣡नाम्, वायूना꣡म् or वायू꣡नाम्, कर्तॄणा꣡म् or कर्तॄ꣡णाम् (see 6.1.54. It might be objected, that नाम् is not preceded by a short vowel, as is shown in the above examples, then how can the anuvritti of ह्रस्व 'short or light vowel' be read into this sutra ? The reply is that the anuvritti of मतुप् should also be read into this sutra, the meaning being "a stem which has a light vowel when followed by मतुप्, will cause the नाम् acute, though the light vowel may become heavy before this ending, in its present form". Otherwise, this rule will apply to forms like तिसॄणा꣡म्, चतसॄणा꣡म् having light vowels before नाम् and not to the forms above given. Why do we read नाम् with the सुट् augment 7.1.54 and not आम्? The rule will not apply to धेन्वाम्꣡ शकट्याम् which get the acute on the final by 6.1.174. Why do we say 'after a stem ending in a light vowel'? Observe कुमारीणा꣡म् (the word कुमार꣡ is end-acute by Un III.138 and so is कुमारी꣡ by 6.1.161. Why do we say after an oxytoned word? Observe त्र꣡पूणाम्, व꣡सूनाम् the words त्रपु and वसु have acute on the first syllable.