Used to convert the pathway-to-vertex id mapping in one CoNetwork
        to the one used in the current CoNetwork (`self`).
        The following tasks are carried out in the remapping:
        (1) If `self.pathways` contains the pathway to be merged, map the
            vertex id in `other_pathway_mapping` to the vertex id
            in `self.pathways`.
        (2) If not, create a vertex in `self` and then add the key-value pair
            to `self.pathways` accordingly.

        Parameters
        -----------
        other_pathway_mapping : dict(str -> int)
          the `pathways` field in the CoNetwork class. This is a
          (pathway -> vertex id) map.

        Returns
        -----------
        dict(int -> int), the (other vertex id -> `self` vertex id)
          conversion map

def convert_pathway_mapping(self, other_pathway_mapping):
        """Used to convert the pathway-to-vertex id mapping in one CoNetwork
        to the one used in the current CoNetwork (`self`).
        The following tasks are carried out in the remapping:
        (1) If `self.pathways` contains the pathway to be merged, map the
            vertex id in `other_pathway_mapping` to the vertex id
            in `self.pathways`.
        (2) If not, create a vertex in `self` and then add the key-value pair
            to `self.pathways` accordingly.

        Parameters
        -----------
        other_pathway_mapping : dict(str -> int)
          the `pathways` field in the CoNetwork class. This is a
          (pathway -> vertex id) map.

        Returns
        -----------
        dict(int -> int), the (other vertex id -> `self` vertex id)
          conversion map
        """
        vertex_id_conversion = {}
        for pathway, vertex_id in other_pathway_mapping.items():
            if pathway in self.pathways:
                vertex_id_conversion[vertex_id] = self.pathways[pathway]
            else:
                self_vertex_id = self.add_pathway(pathway)
                self.vertices[self_vertex_id] = Vertex(self_vertex_id)
                vertex_id_conversion[vertex_id] = self_vertex_id
        return vertex_id_conversion