{
  "objectType": "activity",
  "verb": "undo",
  "id": "tag:example.com,2001:3579",
  "url": "http://example.com/undo/repost",
  "actor": "tag:example.com,2001:alice",
  "object": {
    "objectType": "activity",
    "verb": "share",
    "actor": "tag:example.com,2001:alice",
    "object": "tag:example.com,2001:2468"
  }
}
