input: Write a function to return a substring from a given string using the specified start and end indices. If the start index is greater than the end index, the function should return an empty string.
  def slicing(string, start, end):
      if start > end:
          return ""
      return string[start:end]
  
  assert slicing("This is a slicing test", 8, 15)=="slicing"
  assert slicing("This is a slicing test", 2, 9)=="is is a"
  assert slicing("This is a slicing test", 16, 7)==""
  assert slicing("This is a slicing test", 0, 4)=="This"
  assert slicing("This is a slicing test", 5, 5)==""
output: def slicing(string, start, end):
      if start > end:
          return ""
      return string[start:end]