input: Write a python function to find all possible combinations of words that can be formed with a set of characters.
  assert find_combinations("abcd") == {'ac', 'bd', 'bc', 'ab', 'cd', 'ad', 'db', 'dc'}
  assert find_combinations("a") == set()
  assert find_combinations("ab") == {'ab', 'ba'}
output: def find_combinations(s):
      from itertools import permutations
      return {''.join(p) for p in permutations(s, 2)}