pen in vs restrict

pen in

verb
  • To cause to be stuck in a situation; to be forced into a situation by circumstances. 

  • To enclose (animals) in a pen. 

  • To schedule; fix a date for. 

restrict

verb
  • To restrain within boundaries; to limit; to confine 

  • To consider (a function) as defined on a subset of its original domain. 

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