@Override
		public RedBlackEntry<K, V> previous() {
			if (modCount != expectedModCount) {
				throw new ConcurrentModificationException();
			}
			if (previousNode == null) {
				return null;
			}
			lastReturnedNode = previousNode;
			nextNode = previousNode;
			previousNode = forward ? previousNode.getPredecessor() : previousNode.getSuccessor();
			return lastReturnedNode;
		}
Swap the linkages of two nodes in a tree.
Ghidra/Framework/Generic/src/main/java/ghidra/util/datastruct/RedBlackTree.java