cooccurrence vs coöccurrence

cooccurrence

noun
  • The fact of a thing occurring simultaneously with something else; correlation. 

  • An instance of a thing occurring simultaneously with something else; coincidence. 

coöccurrence

noun
  • The fact of a thing occurring simultaneously with something else; correlation. 

  • An instance of a thing occurring simultaneously with something else; coïncidence. 

How often have the words cooccurrence and coöccurrence occurred in a corpus of books? (source: Google Ngram Viewer )