input: 
  from typing import List
  
  def find_pair(lst: List[int], target: int) -> List[int]:
      """Given a list of numbers and a target number, find a pair of numbers from the 
      given list that add up to the given target.
      >>> find_pair([1, 2, 3, 4, 4, 5, 6], 8)
      [2, 6]
      >>> find_pair([1, 3, 4, 7], 7)
      [3, 4]
      """
      for i in range(len(lst)):
          if (target - lst[i]) in lst[i+1:]:
              return [lst[i], target-lst[i]]
      return []
  
output:     seen = set()
      for num in lst:
          complement = target - num
          if complement in seen:
              return [complement, num]
          seen.add(num)
      return []