closing vs introduction

closing

noun
  • The act by which something is closed. 

  • In morphology, the erosion of the dilation of a set. 

  • The final procedure in a house sale, when documents are signed and recorded. 

  • The end or conclusion of something. 

adj
  • Pertaining to the finish or ending of a series of events; occurring at the end or after all others. 

introduction

noun
  • The act or process of introducing. 

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

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

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

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