input: def removeDuplicates(input: list) -> list:
      """Remove duplicate entries from a list and return the unique elements in the order of their first appearance.
      >>> removeDuplicates([1, 2, 2, 3, 3, 4])
      [1, 2, 3, 4]
      >>> removeDuplicates([4, 4, 5, 5, 6, 6])
      [4, 5, 6]
      """
output:     seen = set()
      result = []
      for item in input:
          if item not in seen:
              seen.add(item)
              result.append(item)
      return result