2-3 Trees
	• 2-3 trees permit the number of children of an internal node to vary between two and three. • This feature allows us to "absorb" insertions and deletions without destroying the tree's shape. – We can therefore search a 2-3 tree almost as efficiently as you can search a minimum-height binary search tree...and it is far easier to maintain a 2-3 tree than it is to guarantee a binary search tree having minimum height.