be up to vs cannot

be up to

verb
  • To do or be involved in doing; to do (often something mischievous or inappropriate). 

  • To depend on, to be the choice of. 

cannot

verb
  • Can not (be unable to). 

  • Be forbidden or not permitted to 

noun
  • Something that cannot be done. 

  • A person who cannot do (something). 

How often have the words be up to and cannot occurred in a corpus of books? (source: Google Ngram Viewer )