In this Kata, you will be given two strings `a` and `b` and your task will be to return the characters that are not common in the two strings. 
For example:
```Haskell
solve("xyab","xzca") = "ybzc" 
--The first string has 'yb' which is not in the second string. 
--The second string has 'zc' which is not in the first string. 
```
Notice also that you return the characters from the first string concatenated with those from the second string.
More examples in the tests cases. 
Good luck!
Please also try [Simple remove duplicates](https://www.codewars.com/kata/5ba38ba180824a86850000f7)
def solve(a, b):
    return "".join(c for c in a + b if c in set(a) ^ set(b))
def solve(a, b):
    return "".join(c for c in a + b if c in set(a) ^ set(b))