Library is related to Borrow. Borrow is related to Debt. Debt is the opposite of Money. Money is related to Safe. 
Professor is the opposite of Student. Student is a type of Worker. 
Library <--RelatedTo--> Borrow <--RelatedTo--> Debt <--Antonym--> Money <--RelatedTo--> Safe 
Professor <--Antonym--> Student --IsA--> Worker 