paperback vs work of fiction

paperback

noun
  • A book with flexible binding. 

adj
  • Having flexible binding. 

verb
  • To issue or publish (a book) in a paperback edition. 

work of fiction

noun
  • A fictional account; a story. 

  • A fictitious account; an account of events that never took place. 

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