Interval is a synonym of Separation. Difference requires Separation. 
Chocolate is related to Sweet. Sweet is related to Desert. you are likely to find Shadow in/at/on Desert. Shadow is related to Ghost. 
Interval <--Synonym--> Separation <--HasPrerequisite-- Difference 
Chocolate <--RelatedTo--> Sweet <--RelatedTo--> Desert <--AtLocation-- Shadow <--RelatedTo--> Ghost 