input: Write a function to generate all subsequences of a list.
  assert get_subsequences([1, 2, 3]) == [[], [1], [2], [1, 2], [3], [1, 3], [2, 3], [1, 2, 3]]
  assert get_subsequences([4, 5]) == [[], [4], [5], [4, 5]]
  assert get_subsequences([7]) == [[], [7]]
output: def get_subsequences(lst):
      subsequences = [[]]
      for num in lst:
          subsequences += [curr + [num] for curr in subsequences]
      return subsequences