diff -r 98dc2d3a9b1d -r db732f8c083a ucx/avl.c
--- a/ucx/avl.c	Sat Jul 15 20:46:18 2017 +0200
+++ b/ucx/avl.c	Sat Jul 15 22:36:29 2017 +0200
@@ -314,3 +314,43 @@
 size_t ucx_avl_count(UcxAVLTree *tree) {
     return ucx_avl_countn(tree->root);
 }
+
+UcxAVLNode* ucx_avl_pred(UcxAVLNode* node) {
+    if (node->left) {
+        UcxAVLNode* n = node->left;
+        while (n->right) {
+            n = n->right;
+        }
+        return n;
+    } else {
+        UcxAVLNode* n = node;
+        while (n->parent) {
+            if (n->parent->right == n) {
+                return n->parent;
+            } else {
+                n = n->parent;
+            }
+        }
+        return NULL;
+    }
+}
+
+UcxAVLNode* ucx_avl_succ(UcxAVLNode* node) {
+    if (node->right) {
+        UcxAVLNode* n = node->right;
+        while (n->left) {
+            n = n->left;
+        }
+        return n;
+    } else {
+        UcxAVLNode* n = node;
+        while (n->parent) {
+            if (n->parent->left == n) {
+                return n->parent;
+            } else {
+                n = n->parent;
+            }
+        }
+        return NULL;
+    }
+}