cooperation vs exchange of contracts

cooperation

noun
  • The act of cooperating. 

  • Association for mutual benefit, such as for purposes of production or purchase. 

  • Active help from a person, organization, etc., such as an orderly sharing of space or resources. 

exchange of contracts

noun
  • The act of exchanging contracts. 

  • The point or stage at which a conveyancing contract comes into existence between negotiating parties for the carrying out of a disposition of an estate in land; usually requiring the payment of a deposit. 

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