code: def is_at_free(G):
      """Check if a graph is AT-free.
  
      The method uses the `find_asteroidal_triple` method to recognize
      an AT-free graph. If no asteroidal triple is found the graph is
      AT-free and True is returned. If at least one asteroidal triple is
      found the graph is not AT-free and False is returned.
  
      Parameters
      ----------
      G : NetworkX Graph
          The graph to check whether is AT-free or not.
  
      Returns
      -------
      bool
          True if G is AT-free and False otherwise.
  
      Examples
      --------
      >>> G = nx.Graph([(0, 1), (0, 2), (1, 2), (1, 3), (1, 4), (4, 5)])
      >>> nx.is_at_free(G)
      True
  
      >>> G = nx.cycle_graph(6)
      >>> nx.is_at_free(G)
      False
      """
      return find_asteroidal_triple(G) is None
  
imports: import networkx
  from networkx.utils import not_implemented_for
label_desc: Use image node_id 2 for calling a global function with example usage: is_at_free(G) and returns: unknown