interrelate vs pertain

interrelate

verb
  • To form relationships between multiple things. 

pertain

verb
  • To relate, to refer, be relevant to. 

  • To apply; to be or remain in place; to continue to be applicable. 

  • To belong to or be a part of; be an adjunct, attribute, or accessory of. 

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