Add set operations. Union, intersect and difference

snippets/array-union.md

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+### Array union
+
+Create a `Set` with all values of `a` and `b` and convert to an array.
+
+```js
+const union = (a, b) => Array.from(new Set([...a, ...b]))
+// union([1,2,3], [4,3,2]) -> [1,2,3,4]
+```