{
  "definitions": {
    "a": {"type": "object", "properties": {
      "toB": {"$ref": "#/definitions/b"},
      "toC": {"$ref": "#/definitions/c"}}},
    "b": {"type": "object", "properties": {
      "backToA": {"$ref": "#/definitions/a"}}},
    "c": {"type": "object", "properties": {
      "backToA": {"$ref": "#/definitions/a"},
      "alsoB":   {"$ref": "#/definitions/b"}}}
  }
}