def headsetofconnecteds(self, ixs):
    '\n        subset of connected list of ixs so that no node has a descendant in it\n\n        By "connected list" we mean that if an ancestor and a descendant are in\n        the list, then so is at least one path connecting them.\n        '
    raise NotImplementedError()
subset of connected list of ixs so that no node has a descendant in it

By "connected list" we mean that if an ancestor and a descendant are in
the list, then so is at least one path connecting them.
def headsetofconnecteds(self, ixs):
    '\n        subset of connected list of ixs so that no node has a descendant in it\n\n        By "connected list" we mean that if an ancestor and a descendant are in\n        the list, then so is at least one path connecting them.\n        '
    raise NotImplementedError()