input: from typing import List
  
  def insert_between_elements(numbers: List[int], separator: int) -> List[int]:
      """ Place a number 'separator' between each pair of elements in the provided list `numbers'
      >>> insert_between_elements([], 4)
      []
      >>> insert_between_elements([1, 2, 3], 4)
      [1, 4, 2, 4, 3]
      """
output:     if not numbers:
          return numbers
      result = []
      for i in range(len(numbers) - 1):
          result.append(numbers[i])
          result.append(separator)
      result.append(numbers[-1])
      return result