preamble vs prolog

preamble

noun
  • A short preliminary statement or remark, especially an explanatory introduction to a formal document or statute. 

  • A syncword. 

verb
  • To speak or write a preamble; to provide a preliminary statement or set of remarks. 

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 preamble and prolog occurred in a corpus of books? (source: Google Ngram Viewer )