Adding clarification on RotateleftChild.

Author: Clément

source/diag/gra/avltree_example_1.txt

@@ -0,0 +1,6 @@
+%%% An AVL tree
+
+A((12))-->B((10))
+A-->C((13))
+B-->D((9))
+B~~~H1:::hidden

source/diag/gra/avltree_example_2.txt

@@ -0,0 +1,10 @@
+%%% An AVL tree before rebalancing using RotateleftChild on a subtree
+
+A((12))-->B((10))
+A-->C((13))
+B-->D((9))
+D-->E((8))
+B~~~H1:::hidden
+D~~~H2:::hidden
+
+

source/diag/gra/avltree_example_3.txt

@@ -0,0 +1,10 @@
+%%% An AVL tree after rebalancing using RotateleftChild on a subtree
+
+A((12))-->B((9))
+A-->C((13))
+B-->D((8))
+B-->E((10))
+E-->F((null))
+E~~~H1:::hidden
+
+

source/diag/gra/avltree_subtree_1.txt

@@ -0,0 +1,6 @@
+%%% An AVL tree
+
+A((10))-->B((9))
+A~~~H1:::hidden
+B~~~H2:::hidden
+B-->E((null))

source/diag/gra/avltree_subtree_2.txt

@@ -0,0 +1,6 @@
+%%% An AVL tree
+
+A((9))~~~H1:::hidden
+A-->B((10))
+B-->C((null))
+B~~~H2:::hidden

source/lectures/data/AVLtrees.md

@@ -67,3 +67,31 @@ It is also possible to compute the height of nodes "on the fly" instead of stori
 - inheriting from the `BTree` class [explored previously](./lectures/data/trees),
 - adding an `IBTree` class that allows you to explore the re-balancing methods more freely,
 - containing some examples showcasing how re-balancing works.
+
+### Additional Example
+
+Consider the following example:
+
+!include diag/gra/avltree_example_1.md
+
+After inserting 8, the tree would become un-balanced and require to call `RotateleftChild`:
+
+!include diag/gra/avltree_example_2.md
+
+The detail to note here is that `RotateleftChild` is called with 
+
+- `nodeTop` being 10,
+- `nodeLeft` being 9,
+- and `nodeLeft.Right` being `null`,
+
+aka, going from
+
+!include diag/gra/avltree_subtree_1.md
+
+to
+
+!include diag/gra/avltree_subtree_2.md
+
+and since the node with value 8 remains the right child of the node with value 9, we obtain (marking explicitely the `null` node that was manipulated):
+
+!include diag/gra/avltree_example_3.md