Air is a different concept from Vacuum. Vacuum is related to Devil. Devil is a type of Trouble. Trouble is a synonym of Ill. 
Century is related to Measurement. Measurement is related to Population. Population is related to Pop. 
Air <--DistinctFrom--> Vacuum <--RelatedTo--> Devil --IsA--> Trouble <--Synonym--> Ill 
Century <--RelatedTo--> Measurement <--RelatedTo--> Population <--RelatedTo--> Pop 