let up vs proceed

let up

verb
  • To cease or stop (doing something intense). 

  • To cease or stop. 

proceed

verb
  • To be transacted; to take place; to occur. 

  • To come from; to have as its source or origin. 

  • To go on in an orderly or regulated manner; to begin and carry on a series of acts or measures; to act methodically 

  • To take an academic degree. 

  • To be applicable or effective; to be valid. 

  • To move, pass, or go forward or onward; to advance; to carry on 

  • To pass from one point, topic, or stage, to another. 

  • To begin and carry on a legal process. 

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