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I was poking around the source to see how things are implemented and I came across this RT class. I'm very new to Clojure and I don't really know Java at all, though I can sort of tell what's going on when I read it. Anyway, I did some searching and I only ever found "RT" in some posts and questions, but not what it stood for.
RT stands for RunTime. clojure.lang.RT implements the core runtime functionality in Clojure.