code: def get_regulatory_pairs(graph: BELGraph) -> Set[NodePair]:
      
      cg = get_causal_subgraph(graph)
  
      results = set()
  
      for u, v, d in cg.edges(data=True):
          if d[RELATION] not in CAUSAL_INCREASE_RELATIONS:
              continue
  
          if cg.has_edge(v, u) and any(dd[RELATION] in CAUSAL_DECREASE_RELATIONS for dd in cg[v][u].values()):
              results.add((u, v))
  
      return results
docs: Find pairs of nodes that have mutual causal edges that are regulating each other such that ``A -> B`` and
      ``B -| A``.
  
      :return: A set of pairs of nodes with mutual causal edges