{
  "@context": {
    "e": "http://example.org/vocab#",
    "e:next": {"@type": "@id"}
  },
  "@graph": [
    {
      "@id": "_:b1",
      "e:next": "_:b2"
    },
    {
      "@id": "_:b2",
      "e:next": "_:b1"
    }
  ]
}