[{
  "http://example.org/input": [{
    "@index": "g1",
    "@graph": [{
      "http://example.org/value": [{"@value": "x"}]
    }]
  }, {
    "@index": "g1",
    "@graph": [{
      "http://example.org/value": [{"@value": "y"}]
    }]
  }, {
    "@index": "g2",
    "@graph": [{
      "http://example.org/value": [{"@value": "a"}]
    }]
  }, {
    "@index": "g2",
    "@graph": [{
      "http://example.org/value": [{"@value": "b"}]
    }]
  }]
}]