+ n = r;
+ r = n->parent;
+ }
+
+ /* n->left == NULL && r == NULL => t is root and has no next
+ * r->right != n => r->left = n => r->parent == NULL */
+ if ((r == NULL) || (r->right != n))
+ {
+ assert ((r == NULL) || (r->parent == NULL));
+ return (NULL);
+ }
+ else
+ {
+ assert (r->right == n);
+ return (r);