Assertion: node's parent | /r/HasProperty | the root
Facets:
Source sentences:
text: If the parent is the root and now has no elements, then free it and make the merged node the new root (tree becomes shallower)
text: (This rule can only trigger if the parent 2-node is the root, since all other 2-nodes along the way will have been modified to not be 2-nodes.