input: Write a python function to find common elements in two lists.
  assert common_elements([1, 2, 3, 4, 8], [2, 6, 8, 10]) == [2, 8]
  assert common_elements([5, 9, 12, 15], [3, 9, 12, 18]) == [9, 12]
  assert common_elements([1, 3, 5, 7], [2, 4, 6, 8]) == []
output: def common_elements(list1, list2):
      return list(set(list1) & set(list2))