coexistence vs concurrency

coexistence

noun
  • The state of two or more things existing together, usually in a temporal or spatial sense, with or without mutual interaction. 

concurrency

noun
  • The property or an instance of being concurrent; something that happens at the same time as something else. 

  • A property of systems where several processes execute at the same time. 

  • A stretch of road that is shared between two or more numbered or named routes. 

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