Optionally the affixes luṅ (Aorist) and laṭ (Present Tense) come after a verb in denoting past time not belonging to the current day, when the word purā is used in the sentence, provided that the word sma is not used.,
The anuvritti of the word anadyatana which had come to a stop with 3.2.120 manifests itself again in this sutra by a process of jumping over the two intermediate aphorisms. This sort of anuvritti is technically called manduka-pluti 'the leap of a frog' i. e. skipping of several sutras and supplying a word from a previous sutra.
This is an optional rule, so that when lat and lun are not used, the proper tenses, as the case may be, must be employed. As वसन्तीह पुरा छात्राः 'the pupils lived here formerly'. So also, Aorist, अवात्सुः पुरा छात्राः; Imperfect, अवसन्निह पुरा छात्राः; Perfect, ऊषुरिह पुरा छात्राः ।
Why do we say 'when the word स्म is not used'? Observe यजति स्म पुरा युधिष्टिरः 'Yudhishthira did perform a sacrifice formerly'. Here rule 118 ante exerts its influence.,