(Carrano, p. 564)

1. A internal 2-node, which has two children, must contain a single data item whose search key satisfies the same relationships as a 2-node in a 2-3 tree.
2. A internal 3-node, which has three children, must contain two data items whose search key satisfies the same relationships as a 3-node in a 2-3 tree.
3. A internal 4-node, which has four children, must contain three data items whose search keys, S, M, and L satisfy the following relationships (show graphically below):
• S is greater than the left child's search key(s) and less than the middle-left child's search key(s).
• M is greater than the middle-left child's search key(s) and greater than the middle-right child's search key(s).
• L is greater than the middle-right child's search key(s) and greater than the right child's search key(s).
4. A leaf node may contain one, two, or three data items.