Arena can be used for Gathering. Arena is a type of Weapon. 
Auction is a type of Sale. Sale is related to Action. Action is related to Cover. Cover is related to Sock. 
Gathering <--UsedFor-- Arena --IsA--> Weapon 
Auction --IsA--> Sale <--RelatedTo--> Action <--RelatedTo--> Cover <--RelatedTo--> Sock 