Code Golf

First rarest elementGiven two lists, **A** and **B**, return the first element of **A** that appears the fewest times in **B**. For example, ``` A = [1, 2, 3, 4, 5, 6] B = [3, 1, 4, 1, 5, 9] ``` The elements '2' and '6' both appear **0** times in **B**. Because '2' occurs first, your program/function should return 2. (note that '9' appears in B but not in A.) **B** may be empty, but **A** will always have at least 1 element. More examples: ``` A = [1, 2, 3, 4] B = [1, 2, 3, 4, 1, 2, 3, 4, 1, 2] -> 3 A = [1, 2, 3, 4] B = [1, 1, 1, 1, 2, 2, 2, 3, 3, 4] -> 4 A = [4, 8, 15, 16, 23, 42] B = [] -> 4 A = [5] B = [1, 2, 3, 4, 5, 6, 7] -> 5 A = [10] B = [1, 2, 3] -> 10 A = [6, 5, 4, 3, 2, 1] B = [5, 2, 3] -> 6 ```