{
  "type": "project",
  "input": {
    "type": "filter",
    "input": {
      "type": "join",
      "input": [
        {
          "type": "extend",
          "input": {
            "type": "bgp",
            "patterns": []
          },
          "variable": {
            "termType": "Variable",
            "value": "z"
          },
          "expression": {
            "type": "expression",
            "subType": "term",
            "term": {
              "termType": "Literal",
              "value": "4",
              "datatype": {
                "termType": "NamedNode",
                "value": "http://www.w3.org/2001/XMLSchema#integer"
              }
            }
          }
        },
        {
          "type": "bgp",
          "patterns": [
            {
              "type": "pattern",
              "termType": "Quad",
              "subject": {
                "termType": "Variable",
                "value": "s"
              },
              "predicate": {
                "termType": "NamedNode",
                "value": "http://example.org/p"
              },
              "object": {
                "termType": "Variable",
                "value": "v"
              },
              "graph": {
                "termType": "DefaultGraph",
                "value": ""
              }
            }
          ]
        }
      ]
    },
    "expression": {
      "type": "expression",
      "subType": "operator",
      "operator": "=",
      "args": [
        {
          "type": "expression",
          "subType": "term",
          "term": {
            "termType": "Variable",
            "value": "v"
          }
        },
        {
          "type": "expression",
          "subType": "term",
          "term": {
            "termType": "Variable",
            "value": "z"
          }
        }
      ]
    }
  },
  "variables": [
    {
      "termType": "Variable",
      "value": "s"
    },
    {
      "termType": "Variable",
      "value": "v"
    },
    {
      "termType": "Variable",
      "value": "z"
    }
  ]
}