The affix u comes after the roots that have taken the affix san and after all the verbs āśaṃs 'to wish' and bhikṣa 'to beg' in the sense of 'agent having such a habit etc.'.,
The term सन् in the aphorism means Desideratives in the affix सन्, and not the verb, सन् because the verb सन् is never seen with this affix.
As, चिकीर्षुः 'desirous of doing'; जिहीर्षुः 'desirous of taking'; आशंसुः 'desirous'; भिक्षुः 'a beggar'.
The verb आशंस् with the upasarga आ is the verb शसि 'to desire' and not the verb शंसि 'to praise'.,