{ "class": "go.GraphLinksModel",
  "nodeDataArray": [ 
{"key":"G1", "isGroup":true, "pos":"0 0", "size":"200 200"},
{"key":"G2", "isGroup":true, "pos":"200 0", "size":"200 200"},
{"key":"G3", "isGroup":true, "pos":"0 200", "size":"200 200"},
{"key":"G4", "isGroup":true, "pos":"200 200", "size":"200 200"}
 ],
  "linkDataArray": [  ]}

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