Question: Which annual gathering that takes place at Black Rock City did Further Future want to change the  "vanish and leave no trace" principles instilled in those who participate in it 
Sentence (from "Further Future"): The Further Future event, "aspires to be a gathering of people with the common goal to spend time together celebrating the infinite possibilities of the future, without necessarily being shackled to the dictates of the past or the cycles of present-day society."
Relevant evidence: No