code: def get_matrix_index(graph: BELGraph) -> Set[str]:
      
      # TODO: Using HGNC Symbols for now
      return {
          node.name
          for node in graph
          if isinstance(node, CentralDogma) and node.namespace.upper() == 'HGNC'
      }
docs: Return set of HGNC names from Proteins/Rnas/Genes/miRNA, nodes that can be used by SPIA.