Before the tense-affixes of the Perfect that have an indicatory ka [[1.2.5]], for the y of vay may optionally be substituted a v,
Thus ऊयतुः or ऊवतुः, ऊवुः or ऊयुः ॥ According to Patanjali, the phrase वश्चास्य of this sutra could have been dispensed with; this much would have been enough:- अन्यतरस्या किति वेञः ॥ Thus वे + अतुम् = वा + वा + अतुस् = ववतुः and ववुः (the vocalisation being prohibited). In the alternative:-वा + अतुस् = उ +अतुस् = उ + उवङ् + अतुस् 6.1.77 = ऊवतुः, ऊवुः ॥ Here there is vocalisation. In the case of वय् substitute, the य is never vocalised, so we have ऊयतुः, ऊयुः ॥ Thus all the three forms have been evolved without using वश्चास्य ॥,