Editing AVL tree (section)

===Balance factor===
In a [[binary tree]] the ''balance factor'' of a node X is defined to be the height difference

:<math> \text{BF}(X) := \text{Height}(\text{LeftSubtree}(X)) - \text{Height}(\text{RightSubtree}(X)) </math><ref name="Knuth">{{Cite book |last=Knuth |first=Donald E. |title=Sorting and searching |publisher=Addison-Wesley |year=2000 |isbn=0-201-89685-0 |edition=2. ed., 6. printing, newly updated and rev. |location=Boston [u.a.] |author-link=Donald Knuth}}</ref>{{rp|459}}

of its two child sub-trees rooted by node X.

A node X with <math>\text{BF}(X)<0</math> is called "left-heavy", one with <math>\text{BF}(X)>0</math> is called "right-heavy", and one with <math>\text{BF}(X)=0</math> is sometimes simply called "balanced".