code: def get_correlation_graph(graph: BELGraph) -> Graph:
      
      result = Graph()
  
      for u, v, d in graph.edges(data=True):
          if d[RELATION] not in CORRELATIVE_RELATIONS:
              continue
  
          if not result.has_edge(u, v):
              result.add_edge(u, v, **{d[RELATION]: True})
  
          elif d[RELATION] not in result[u][v]:
              log.log(5, 'broken correlation relation for %s, %s', u, v)
              result[u][v][d[RELATION]] = True
              result[v][u][d[RELATION]] = True
  
      return result
docs: Extract an undirected graph of only correlative relationships.