input: Write a function to efficiently process a list and return a new list containing only those elements that are greater than a specified threshold. The function should take in the list and the threshold as arguments and return the new list.
  assert efficient_filter([1, 2, 3, 4], 2) == [3, 4]
  assert efficient_filter([5, 6, 7, 8, 9], 7) == [8, 9]
  assert efficient_filter([10, 11, 12, 13], 12) == [12, 13]
  assert efficient_filter([1, 1, 1, 1], 1) == []
  assert efficient_filter([], 0) == []
output: def efficient_filter(lst, threshold):
      return [x for x in lst if x > threshold]