{
  "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": [
        {
          "type": "expression",
          "subType": "operator",
          "operator": "coalesce",
          "args": [
            {
              "type": "expression",
              "subType": "term",
              "term": {
                "termType": "Variable",
                "value": "x"
              }
            },
            {
              "type": "expression",
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              "term": {
                "termType": "Variable",
                "value": "g"
              }
            }
          ]
        },
        {
          "type": "expression",
          "subType": "term",
          "term": {
            "termType": "Variable",
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          }
        }
      ]
    }
  },
  "variables": [
    {
      "termType": "Variable",
      "value": "g"
    },
    {
      "termType": "Variable",
      "value": "o"
    },
    {
      "termType": "Variable",
      "value": "p"
    },
    {
      "termType": "Variable",
      "value": "x"
    }
  ]
}