code: def ramsey_R2(G):
      r"""Compute the largest clique and largest independent set in `G`.
  
      This can be used to estimate bounds for the 2-color
      Ramsey number `R(2;s,t)` for `G`.
  
      This is a recursive implementation which could run into trouble
      for large recursions. Note that self-loop edges are ignored.
  
      Parameters
      ----------
      G : NetworkX graph
          Undirected graph
  
      Returns
      -------
      max_pair : (set, set) tuple
          Maximum clique, Maximum independent set.
  
      Raises
      ------
      NetworkXNotImplemented
          If the graph is directed or is a multigraph.
      """
      if not G:
          return set(), set()
  
      node = arbitrary_element(G)
      nbrs = (nbr for nbr in nx.all_neighbors(G, node) if nbr != node)
      nnbrs = nx.non_neighbors(G, node)
      c_1, i_1 = ramsey_R2(G.subgraph(nbrs).copy())
      c_2, i_2 = ramsey_R2(G.subgraph(nnbrs).copy())
  
      c_1.add(node)
      i_2.add(node)
      # Choose the larger of the two cliques and the larger of the two
      # independent sets, according to cardinality.
      return max(c_1, c_2, key=len), max(i_1, i_2, key=len)
  
imports: import networkx
  from networkx.utils import not_implemented_for
  from ...utils import arbitrary_element
label_desc: Use image node_id 1 for calling a global function with example usage: ramsey_R2(G) and returns: max,  max, set,  set