The final o of a particle is a pragṛhya,
This sútra consists of one word ओत् the final त् is a surplusage. The words \pragrihya\ and \nipåta\ are to be supplied from the preceding sutras to complete the sense. The meaning is that those particles which end in ओ though consisting of several letters, are pragrihya. As अहो अपेहि \Halloo, go away.\,
