{
  "type": "project",
  "input": {
    "type": "filter",
    "input": {
      "type": "bgp",
      "patterns": [
        {
          "type": "pattern",
          "termType": "Quad",
          "subject": {
            "termType": "Variable",
            "value": "x"
          },
          "predicate": {
            "termType": "NamedNode",
            "value": "http://example.com/p"
          },
          "object": {
            "termType": "Variable",
            "value": "n"
          },
          "graph": {
            "termType": "DefaultGraph",
            "value": ""
          }
        }
      ]
    },
    "expression": {
      "type": "expression",
      "subType": "existence",
      "not": true,
      "input": {
        "type": "filter",
        "input": {
          "type": "bgp",
          "patterns": [
            {
              "type": "pattern",
              "termType": "Quad",
              "subject": {
                "termType": "Variable",
                "value": "x"
              },
              "predicate": {
                "termType": "NamedNode",
                "value": "http://example.com/q"
              },
              "object": {
                "termType": "Variable",
                "value": "m"
              },
              "graph": {
                "termType": "DefaultGraph",
                "value": ""
              }
            }
          ]
        },
        "expression": {
          "type": "expression",
          "subType": "operator",
          "operator": "=",
          "args": [
            {
              "type": "expression",
              "subType": "term",
              "term": {
                "termType": "Variable",
                "value": "n"
              }
            },
            {
              "type": "expression",
              "subType": "term",
              "term": {
                "termType": "Variable",
                "value": "m"
              }
            }
          ]
        }
      }
    }
  },
  "variables": [
    {
      "termType": "Variable",
      "value": "n"
    },
    {
      "termType": "Variable",
      "value": "x"
    }
  ]
}