beleaguer vs work on

beleaguer

verb
  • To besiege; to surround with troops. 

  • To exhaust. 

  • To vex, harass, or beset. 

work on

verb
  • To shape, form or improve something. 

  • To exercise influence on someone. 

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