Mainstream is a synonym of Common. Common is a different concept from Special. Special is a synonym of Extra. 
Set is a synonym of Time. Time is related to Division. Division is related to Season. 
Mainstream <--Synonym--> Common <--DistinctFrom--> Special <--Synonym--> Extra 
Set <--Synonym--> Time <--RelatedTo--> Division <--RelatedTo--> Season 