arango> db.relation.inEdges("vertex/1528086");
[ ]
arango> db.relation.inEdges("vertex/1593622");
[
  {
    "_id" : "inEdges/3100950",
    "_key" : "3100950",
    "_rev" : "3100950", 
    "_from" : "vertex/1528086",
    "_to" : "vertex/1593622",
    "label" : "knows"
  }
]