On: 2 is a code smell

[Jach]

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tl;dr Clojure is awesome. And use

    (defn add-vectors [& vs]
     (vec (apply map + vs)))

instead of

    (defn add-vectors [va vb]
     [(+ (first va) (first vb)) (+ (second va) (second vb))])

since in Clojure code that operates on 1 or N things is usually better than some other fixed value. (Like 2.)