{
  "type": "project",
  "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": "filter",
        "input": {
          "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"
    }
  ]
}