Write first_letters(words) returning a sorted list of the distinct lower-case first letters (build a set with a comprehension first).
first_letters(['Apple', 'avocado', 'Banana', '']) → ['a', 'b']
first_letters([]) → []
Submit runs 3 tests, including hidden edge cases.
Each hint gives a little more help. Try on your own first.
Run your code to see the output here.