The rebalancing loop of the delete operation has the following invariant: At the beginning of each iteration the black height of N equals the iteration number minus one, which means that in the first iteration it is zero and that N is a true black node 13px in higher iterations. The number of black nodes on the paths through N is one less than before the deletion, whereas it is unchanged on all other paths, so that there is a black-violation at P if other paths exist. All other properties (including requirement 3) are satisfied throughout the tree.
The rebalancing loop of the delete operation has the following invariant At the beginning of each iteration the black height of N equals the iteration number minus one which means that in the first iteration it is zero and that N is a true black node 13px in higher iterations The number of black nodes on the paths through N is one less than before the deletion whereas it is unchanged on all other paths so that there is a black-violation at P if other paths exist All other properties (including requirement 3) are satisfied throughout the tree