keep up vs remain

keep up

verb
  • To continue with (work, etc). 

  • To maintain; to preserve; to prevent from deteriorating. 

  • To stay even or ahead. 

  • To ensure that one remains well-informed about something. 

  • To prevent someone from going to bed or to sleep 

remain

verb
  • To continue in a state of being. 

  • To await; to be left to. 

  • To continue unchanged in place, form, or condition, or undiminished in quantity; to abide; to stay; to endure; to last. 

  • To be left after a number or quantity has been subtracted or cut off; to be left as not included or comprised. 

  • To stay after others or other parts have been removed or otherwise disappeared. 

noun
  • That which is left; relic; remainder. 

  • That which is left of a human being after the life is gone; relics; a dead body. 

  • Posthumous works or productions, especially literary works. 

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