docs: def lines_from_tree(tree, nodes_and_set:bool=False) -> iter:
      """Yield lines of bubble describing given BubbleTree"""
      NODE = 'NODE\t{}'
      INCL = 'IN\t{}\t{}'
      EDGE = 'EDGE\t{}\t{}\t1.0'
      SET  = 'SET\t{}'
  
      if nodes_and_set:
          for node in tree.nodes():
              yield NODE.format(node)
  
          for node in tree.powernodes():
              yield SET.format(node)
  
      for node, includeds in tree.inclusions.items():
          for included in includeds:
              yield INCL.format(included, node)
  
      for node, succs in tree.edges.items():
          for succ in succs:
              yield EDGE.format(node, succ)