As a positional structure, our TreeMap implementation has a subtle flaw. A position instance p associated with an key-value pair ( k , v ) should remain valid as long as that item remains in the map....

A position instance
p
associated with an key-value pair (k,v) should remain

valid as long as that item remains in the map. In particular, that

position should be unaffected by calls to insert or delete other items in the

collection. Our algorithm for deleting an item from a binary search tree

may fail to provide such a guarantee, in particular because of our rule for

using the inorder predecessor of a key as a replacement when deleting a

key that is located in a node with two children. Given an explicit series of

Python commands that demonstrates such a flaw.