anchor.diff:                "http://example.root/A"
                 "http://example.root/A2" "http://example.root/A1")))
   
  +;; TODO: Irrelevant?
   ;; (prove:subtest
   ;;     "Reorder manually set current node."
  -;;   (prove:is (htree:all-nodes-data
  +;;   (prove:is (htree:all-contiguous-owned-nodes-data
   ;;              (let* ((history (make-tree2))
   ;;                     (second-child (second (htree:children
  -;;                                            (htree:current (htree:back history))))))
  -;;                (setf (htree:current history) second-child)
  +;;                                            (htree:current-owner-node (htree:back history))))))
  +;;                (setf (htree:current-owner-node history) second-child)
   ;;                (htree:back history)
   ;;                history))
   ;;             '("http://example.root"
   ;;               "http://example.root/A"
   ;;               "http://example.root/B")))
   
  -;; (prove:subtest
  -;;     "Traverse all history."
  -;;   (prove:is (htree:all-nodes-data
  -;;              (htree:back (make-tree1)))
  -;;             '("http://example.root"
  -;;               "http://example.root/B"
  -;;               "http://example.root/B2" "http://example.root/B1"
  -;;               "http://example.root/A"
  -;;               "http://example.root/A2" "http://example.root/A1")))
  -
  -;; (prove:subtest
  -;;     "Traverse parents."
  -;;   (prove:is (htree:parent-nodes-data
  -;;              (htree:back (make-tree1)))
  -;;             '("http://example.root")))
  -
  -;; (prove:subtest
  -;;     "Traverse forward children."
  -;;   (prove:is (htree:forward-children-nodes-data
  -;;              (htree:back (make-tree1)))
  -;;             '("http://example.root/B2")))
  +(prove:subtest "Traverse parents."
  +  (prove:is (htree:parent-nodes-data
  +             (htree:back (make-tree1)))
  +            '("http://example.root")))
  +
  +(prove:subtest "Traverse forward children."
  +  (prove:is (htree:forward-children-nodes-data
  +             (htree:back (make-tree1)))
  +            '("http://example.root/B2")))
   
   ;; (prove:subtest
   ;;     "Traverse all children."
  
positive.code:     (htree:add-child "http://example.root/B2" tree)
      tree))
  
  ;; (defun make-tree2 ()
  ;;   (let ((tree (htree:make)))
  ;;     (htree:add-child "http://example.root" tree)
  ;;     (htree:add-child "http://example.root/A" tree)
  ;;     (htree:back tree)
  ;;     (htree:add-child "http://example.root/B" tree)
  ;;     tree))
  
  (prove:subtest "Single entry"
    (let ((history (htree:make))
  
negative.code:     ;; TODO: Go to other child.
      ))
  
  (prove:subtest "Simple branching tree tests."
    (prove:is (htree:value (htree:current-owner-node (make-tree1)))
              "http://example.root/B2"))
  
  (prove:subtest "History depth."
    (prove:is (htree:depth (make-tree1))
              2))
  
  (prove:subtest "History size."
    (prove:is (htree:size (make-tree1))
              7))
  
  (prove:subtest "All contiguous history nodes for current owner."
    (prove:is (htree:all-contiguous-owned-nodes-data (make-tree1))
              '("http://example.root"
                "http://example.root/B"
  