{
  "type": "project",
  "input": {
    "type": "filter",
    "input": {
      "type": "bgp",
      "patterns": [
        {
          "type": "pattern",
          "termType": "Quad",
          "subject": {
            "termType": "Variable",
            "value": "x"
          },
          "predicate": {
            "termType": "Variable",
            "value": "p"
          },
          "object": {
            "termType": "Variable",
            "value": "o"
          },
          "graph": {
            "termType": "Variable",
            "value": "g"
          }
        }
      ]
    },
    "expression": {
      "type": "expression",
      "subType": "operator",
      "operator": "=",
      "args": [
        {
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          "subType": "operator",
          "operator": "coalesce",
          "args": [
            {
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              "operator": "iri",
              "args": [
                {
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                  "operator": "concat",
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                            "termType": "Variable",
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                      ]
                    },
                    {
                      "type": "expression",
                      "subType": "term",
                      "term": {
                        "termType": "Literal",
                        "value": "#graph",
                        "datatype": {
                          "termType": "NamedNode",
                          "value": "http://www.w3.org/2001/XMLSchema#string"
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              ]
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            {
              "type": "expression",
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                "termType": "Variable",
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              }
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          ]
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        {
          "type": "expression",
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            "termType": "Variable",
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          }
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      ]
    }
  },
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    {
      "termType": "Variable",
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    },
    {
      "termType": "Variable",
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    },
    {
      "termType": "Variable",
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    },
    {
      "termType": "Variable",
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  ]
}