input: Write a function to find the common elements between two given lists. If there are no common elements, return an empty list.
  def find_common_elements(list1, list2):
      common = [x for x in list1 if x in list2]
      return common
  assert find_common_elements([1, 2, 3], [2, 3, 4])==[2, 3]
  assert find_common_elements([4, 5, 6], [7, 8, 9])==[]
  assert find_common_elements([1, 2, 3, 4, 5], [5, 4, 3, 2, 1])==[1, 2, 3, 4, 5]
  assert find_common_elements([], [1, 2, 3])==[]
  assert find_common_elements([1, 2, 3], [])==[]
output: def find_common_elements(list1, list2):
      common = [x for x in list1 if x in list2]
      return common