irrevocable vs mandatory

irrevocable

adj
  • Unable to be retracted or reversed; final. 

mandatory

noun
  • A sign or line that require the path of the disc to be above, below or to one side of it. 

adj
  • Of, being or relating to a mandate. 

  • Obligatory; required or commanded by authority. 

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