go ahead vs set to work

go ahead

verb
  • To proceed with; to begin. 

  • Used to grant permission for or to give endorsement of a suggestion or proposal. 

  • To send communication over the radio. 

set to work

verb
  • To begin working. 

  • To cause to begin working. 

  • To begin working at. 

How often have the words go ahead and set to work occurred in a corpus of books? (source: Google Ngram Viewer )