## conjEdit

```
user=> (conj [1 2 3] 4)
[1 2 3 4]
user=> (conj '(:a :b :c) \d)
(\d :a :b :c)
```

## concatEdit

```
(defn poly-expand
poly-expand [points]
(loop [aa (first points) remaining (rest points) built (empty points)]
(if (empty? remaining)
(concat built [aa (first points)])
(recur (first remaining) (rest remaining)
(concat built [aa (first remaining)])))))
(poly-expand '[a b c d])
-> [a b b c c d d a]
```

## mergeEdit

Combine two maps into a more massive map

`(merge {:a 1} {:b 2}) => {:a 1, :b 2}) (merge-with + {:a 1} {:a 2, :b 3}) => {:a 3 :b 3}`