[
  {
    "@id": "_:a",
    "@type": ["http://example.com/SubType"]
  },
  {
    "@id": "http://example.com/Subj1",
    "@type": ["http://example.com/Type"],
    "http://example.com/ref": [
      {"@id": "_:a"},
      {"@id": "http://example.com/Subj2"}
    ]
  },
  {
    "@id": "http://example.com/Subj2",
    "@type": ["http://example.com/Type"],
    "http://example.com/ref": [{"@id": "http://example.com/Subj1"}]
  }
]