{
  "type": "project",
  "input": {
    "type": "filter",
    "input": {
      "type": "bgp",
      "patterns": [
        {
          "type": "pattern",
          "termType": "Quad",
          "subject": {
            "termType": "Variable",
            "value": "s"
          },
          "predicate": {
            "termType": "Variable",
            "value": "p"
          },
          "object": {
            "termType": "NamedNode",
            "value": "http://www.example.org/o1"
          },
          "graph": {
            "termType": "NamedNode",
            "value": "http://www.example.org/graph"
          }
        }
      ]
    },
    "expression": {
      "type": "expression",
      "subType": "existence",
      "not": false,
      "input": {
        "type": "bgp",
        "patterns": [
          {
            "type": "pattern",
            "termType": "Quad",
            "subject": {
              "termType": "Variable",
              "value": "s"
            },
            "predicate": {
              "termType": "Variable",
              "value": "p"
            },
            "object": {
              "termType": "NamedNode",
              "value": "http://www.example.org/o2"
            },
            "graph": {
              "termType": "NamedNode",
              "value": "http://www.example.org/graph"
            }
          }
        ]
      }
    }
  },
  "variables": [
    {
      "termType": "Variable",
      "value": "p"
    },
    {
      "termType": "Variable",
      "value": "s"
    }
  ]
}