code: def expand_internal_causal(universe: BELGraph, graph: BELGraph) -> None:
      
      expand_internal(universe, graph, edge_predicates=is_causal_relation)
docs: Add causal edges between entities in the sub-graph.
  
      Is an extremely thin wrapper around :func:`expand_internal`.
  
      :param universe: A BEL graph representing the universe of all knowledge
      :param graph: The target BEL graph to enrich with causal relations between contained nodes
  
      Equivalent to:
  
      >>> from pybel_tools.mutation import expand_internal
      >>> from pybel.struct.filters.edge_predicates import is_causal_relation
      >>> expand_internal(universe, graph, edge_predicates=is_causal_relation)