{
  "solar_system/phobos" => [
    [0] "solar_system/body",
    [1] "solar_system/mars"
  ],
  "solar_system/body"   => [],
  "solar_system/mars"   => [
    [0] "solar_system/planet"
  ],
  "solar_system/planet" => [
    [0] "solar_system/body"
  ]
}