a
a has two uses: an interjection and an emphatic particle. As an interjection, it’s very broad; it can indicate a pause for thought, a realization when learning something, astonishment at a fact, and more.
a, mi sona ala e ni.
As an emphatic particle, it’s narrower, emphasizing the phrase that it’s placed after or the entire sentence if it’s at the end.
ona li wile a e ilo sin ni.