{
  "version": "0.1",
  "nodes": {
    "1": { "id": 1, "name": "outer_cube", "op": {"type": "Cube", "size": {"x": 40, "y": 40, "z": 80}} },
    "2": { "id": 2, "name": "outer_centered", "op": {"type": "Translate", "child": 1, "offset": {"x": -20, "y": -20, "z": 0}} },
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    "4": { "id": 4, "name": "inner_centered", "op": {"type": "Translate", "child": 3, "offset": {"x": -14, "y": -14, "z": 0}} },
    "5": { "id": 5, "name": "hollow_tube", "op": {"type": "Difference", "left": 2, "right": 4} }
  },
  "materials": {},
  "part_materials": {},
  "roots": [{ "root": 5, "material": "default" }]
}