correspondence vs level set

correspondence

noun
  • A relation. 

  • Reciprocal exchange of civilities, especially conversation between persons by means of letters. 

  • Postal or other written communications. 

  • An agreement of situations or objects with an expected outcome. 

  • Newspaper or news stories. 

  • A similarity between physical and spiritual things (e.g. light to wisdom, or warmth to love) 

level set

noun
  • A state of mutual understanding among parties 

  • An event consisting of level setting 

  • The set of values x for which a real-valued function f(x) is equal to a given constant. 

verb
  • To establish a baseline of mutual understanding 

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