code: def is_BF_hypergraph(self):
          
          for hyperedge_id in self._hyperedge_attributes:
              tail = self.get_hyperedge_tail(hyperedge_id)
              head = self.get_hyperedge_head(hyperedge_id)
              if len(tail) > 1 and len(head) > 1:
                  return False
          return True
docs: Indicates whether the hypergraph is a BF-hypergraph.
          A BF-hypergraph consists of only B-hyperedges and F-hyperedges.
          See "is_B_hypergraph" or "is_F_hypergraph" for more details.
  
          :returns: bool -- True iff the hypergraph is an F-hypergraph.