text: class Helpers(object):
    """
    Adds additional helper functions that aren't part of the core or extended
    API.
    """
  
    def __init__(self, api):
      self.api = api
  
    def is_promotable(self, tail):
      # type: (TransactionHash) -> bool
      """
      Determines if a tail transaction is promotable.
  
      :param tail:
        Transaction hash. Must be a tail transaction.
      """
      return self.api.check_consistency(tails=[tail])['state']
  