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union 

        # Array.union

(from ruby core)
---
    array.union(*other_arrays) -> new_array

---

Returns a new Array that is the union of `self` and all given Arrays
`other_arrays`; duplicates are removed;  order is preserved;  items are
compared using `eql?`:
    [0, 1, 2, 3].union([4, 5], [6, 7]) # => [0, 1, 2, 3, 4, 5, 6, 7]
    [0, 1, 1].union([2, 1], [3, 1]) # => [0, 1, 2, 3]
    [0, 1, 2, 3].union([3, 2], [1, 0]) # => [0, 1, 2, 3]

Returns a copy of `self` if no arguments given.

Related: Array#|.

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