code: def is_arborescence(G):
      """
      Returns True if `G` is an arborescence.
  
      An arborescence is a directed tree with maximum in-degree equal to 1.
  
      Parameters
      ----------
      G : graph
          The graph to test.
  
      Returns
      -------
      b : bool
          A boolean that is True if `G` is an arborescence.
  
      Examples
      --------
      >>> G = nx.DiGraph([(0, 1), (0, 2), (2, 3), (3, 4)])
      >>> nx.is_arborescence(G)
      True
      >>> G.remove_edge(0, 1)
      >>> G.add_edge(1, 2)  # maximum in-degree is 2
      >>> nx.is_arborescence(G)
      False
  
      Notes
      -----
      In another convention, an arborescence is known as a *tree*.
  
      See Also
      --------
      is_tree
  
      """
      return is_tree(G) and max(d for n, d in G.in_degree()) <= 1
  
imports: import networkx
label_desc: Use image node_id 1 for calling a global function with example usage: is_arborescence(G) and returns: unknown