## Which Are In?

Given two arrays of strings a1 and a2 return a sorted array r in lexicographical order of the strings of a1 which are substrings of strings of a2.

**Example 1:**
```
a1 = ["arp", "live", "strong"]

a2 = ["lively", "alive", "harp", "sharp", "armstrong"]

returns ["arp", "live", "strong"]
```
**Example 2:**
```
a1 = ["tarp", "mice", "bull"]

a2 = ["lively", "alive", "harp", "sharp", "armstrong"]

returns []
```
**Notes:**

Arrays are written in "general" notation. See "Your Test Cases" for examples in your language.
In Shell bash a1 and a2 are strings. The return is a string where words are separated by commas.
Beware: r must be without duplicates.