input: Write a function to slice a string based on given start and end indices, and return the resulting substring. The function should take three parameters: the string, the start index, and the end index. If the start index is greater than the end index, the function should return the empty string.
  assert slicing("This is a slicing test", 8, 15)=="s a slic"
  assert slicing("This is a slicing test", 0, 4)=="This"
  assert slicing("This is a slicing test", 5, 5)==""
  assert slicing("This is a slicing test", 15, 8)==""
  assert slicing("This is a slicing test", -5, -1)=="test"
output: def slicing(s, start, end):
      if start > end:
          return ""
      return s[start:end]