def _concatenate(*args):
  """
  Reduces a list of a mixture of elements and lists down to a single list.

  Parameters
  ----------
  args : tuple of (object or list of object)

  Returns
  -------
  list
  """
  lst = []
  for arg in args:
    if isinstance(arg, list):
      for elem in arg:
        lst.append(elem)
    else:
      lst.append(arg)
  return lst