fill in vs introduce

fill in

verb
  • To inform somebody, especially to supply someone missing or missed information. 

  • To substitute for somebody or something. 

  • To complete a form or questionnaire with requested information. 

  • To beat up; to physically assault. 

  • To fill; to replace material that is absent or has been removed. 

introduce

verb
  • To make (something or someone) known by formal announcement or recommendation. 

  • To cause (someone) to be acquainted (with someone else). 

  • To add (something) to a system, a mixture, or a container. 

  • To bring (something) into practice. 

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