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<=> 

        # Array.<=>

(from ruby core)
---
    array <=> other_array -> -1, 0, or 1

---

Returns -1, 0, or 1 as `self` is less than, equal to, or greater than
`other_array`. For each index `i` in `self`, evaluates `result = self[i]
<=> other_array[i]`.

Returns -1 if any result is -1:
    [0, 1, 2] <=> [0, 1, 3] # => -1

Returns 1 if any result is 1:
    [0, 1, 2] <=> [0, 1, 1] # => 1

When all results are zero:
*   Returns -1 if `array` is smaller than `other_array`:
        [0, 1, 2] <=> [0, 1, 2, 3] # => -1

*   Returns 1 if `array` is larger than `other_array`:
        [0, 1, 2] <=> [0, 1] # => 1

*   Returns 0 if `array` and `other_array` are the same size:
        [0, 1, 2] <=> [0, 1, 2] # => 0

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