labels: Labels (i.e. names) of the two corpora featured in the graph.
write_to_graph: Flag to indicate whether to write results to the graph (i.e. save citation count values as node attributes).
Returns
If write_to_graph is FALSE, returns a list of entries (authors, title, year, corpus, citations) sorted by decreasing citation count. Else, returns the graph given as input to which citation count values are added as node attributes.