introduction vs prolog

introduction

noun
  • An initial section of a book or article, which introduces the subject material. 

  • A written or oral explanation of what constitutes the basis of an issue. 

  • The act or process of introducing. 

  • A means, such as a personal letter, of presenting one person to another. 

prolog

noun
  • A speech or section used as an introduction, especially to a play or novel. 

  • A component of a computer program that prepares the computer to execute a routine. 

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