input: from typing import List
  
  def deleteDuplicates(numbers: List[float]) -> List[float]:
      """ Deletes all duplicates in a given list of numbers.
      >>> deleteDuplicates([1, 2, 3, 4, 4, 2, 1])
      [1, 2, 3, 4]
      >>> deleteDuplicates([1.0, 2.8, 3.0, 4.0, 2.8, 1.0])
      [1.0, 2.8, 3.0, 4.0]
      """
output:     seen = set()
      result = []
      for num in numbers:
          if num not in seen:
              seen.add(num)
              result.append(num)
      return result