arango> db.demo.getIndexes()
[
  { "id" : "1439003/0", 
    "type" : "primary",
    "fields" : ["_id"]
  }, 
  { 
    "id" : "1439003/2290971", 
    "unique" : true, 
    "type" : "hash", 
    "fields" : ["a"] 
  }, 
  { 
    "id" : "1439003/2946331",
    "unique" : false, 
    "type" : "hash", 
    "fields" : ["b"] 
  },
  { 
    "id" : "1439003/3077403", 
    "unique" : false, 
    "type" : "skiplist", 
    "fields" : ["c"]
  }
]