constrain vs leave alone

constrain

verb
  • To force physically, by strong persuasion or pressuring; to compel; to oblige. 

  • To keep within close bounds; to confine. 

  • To reduce a result in response to limited resources. 

leave alone

verb
  • To desist or refrain from involvement with. 

  • To stop bothering (a person). 

How often have the words constrain and leave alone occurred in a corpus of books? (source: Google Ngram Viewer )