In general it’s the positive or negative of the verb though - were you? I was. Did you? I did. Will you? I will. Did she? She did etc.
So the verb has a negative declension, or is it just some kind of conjunction that negates the verb?
Either way, that's kind of beautiful. English has a problem where one can ask a compound question, and replying "no" doesn't clarify a damn thing. This would be impossible in Irish, since you'd have to pick one or some combination of questions to reply to, as the verb-form is required.