Meaning of 用不説 in Japanese

あなたがなんと言おうと、私はやはりその説が正しいと思う。
For all you say, I still believe in the truth of the theory.

何の用でここに来たのですか。
What has brought you here?

それから服を着て、講義用のメモを手さげ鞄に詰め込み、階段を駆け下りた。
Then he got dressed, stuffed his lecture notes into his briefcase, and ran down the stairs.

無から有は生じない。
Nothing comes from nothing.