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.