503 TREE LOCKING ON CHANGING TREES V. Lanin, D. Shasha, April 1990 The tree locking protocol is a deadlock-free method of concurrency control defined and verified by Silberschatz and Kedem for data organized in a directed tree. Can the tree protocol work for applications that change the tree? We define a set of three operations capable of changing any tree to any other tree and show that the tree protocol continues to ensure serializability and deadlock-freedom in the presence of these operations.