{
  "type": "project",
  "input": {
    "type": "join",
    "input": [
      {
        "type": "leftjoin",
        "input": [
          {
            "type": "bgp",
            "patterns": [
              {
                "type": "pattern",
                "termType": "Quad",
                "subject": {
                  "termType": "Variable",
                  "value": "a"
                },
                "predicate": {
                  "termType": "NamedNode",
                  "value": "http://example.org/ns#b"
                },
                "object": {
                  "termType": "NamedNode",
                  "value": "http://example.org/ns#c"
                },
                "graph": {
                  "termType": "DefaultGraph",
                  "value": ""
                }
              }
            ]
          },
          {
            "type": "bgp",
            "patterns": [
              {
                "type": "pattern",
                "termType": "Quad",
                "subject": {
                  "termType": "NamedNode",
                  "value": "http://example.org/ns#x"
                },
                "predicate": {
                  "termType": "NamedNode",
                  "value": "http://example.org/ns#y"
                },
                "object": {
                  "termType": "NamedNode",
                  "value": "http://example.org/ns#z"
                },
                "graph": {
                  "termType": "DefaultGraph",
                  "value": ""
                }
              }
            ]
          }
        ]
      },
      {
        "type": "bgp",
        "patterns": [
          {
            "type": "pattern",
            "termType": "Quad",
            "subject": {
              "termType": "NamedNode",
              "value": "http://example.org/ns#x"
            },
            "predicate": {
              "termType": "Variable",
              "value": "y"
            },
            "object": {
              "termType": "Variable",
              "value": "z"
            },
            "graph": {
              "termType": "DefaultGraph",
              "value": ""
            }
          }
        ]
      }
    ]
  },
  "variables": [
    {
      "termType": "Variable",
      "value": "a"
    },
    {
      "termType": "Variable",
      "value": "y"
    },
    {
      "termType": "Variable",
      "value": "z"
    }
  ]
}