1. Clojure

2. Calc
(defn calc [op v1 v2]
(cond (= "+" op) (+ v1 v2)
(= "-" op) (- v1 v2)
(= "*" op) (* v1 v2)
(= "/" op) (/ v1 v2)
))

3. Set - Intersection
user=> (clojure.core/refer 'clojure.set)
user=> (def s #{1 2 3 4 })
user=> (def s2 #{3 4 5 6 7})
user=> (intersection s)
#{1 2 3 4}
user=> (intersection s s2)
#{3 4}
user=> (def s3 #{2 3 9 0})
user=> (intersection s s2 s3)
#{3}

4. Set - Difference
user=> (difference s)
#{1 2 3 4}
user=> (difference s s2)
#{1 2}
user=> (difference s s2 s3)
#{1}

5. Set - Union
user=> (union s)
#{1 2 3 4}
user=> (union s s2)
#{1 2 3 4 5 6 7}
user=> (union s s2 s3)
#{0 1 2 3 4 5 6 7 9}