Notion is related to Quality. Quality is related to Level. Level is a synonym of Grade. Grade is related to Hill. 
Restrict is a type of Prevent. Restrict is a synonym of Contain. Contain is related to Keep. 
Notion <--RelatedTo--> Quality <--RelatedTo--> Level <--Synonym--> Grade <--RelatedTo--> Hill 
Prevent <--IsA-- Restrict <--Synonym--> Contain <--RelatedTo--> Keep 