Before revision:  However, at some point in the future, any training data point z \in S can request to be unlearned, thus prompting the learner to modify its output predictor while still ensuring the same accuracy guarantees.
After revision:  However, at some point in the future, any training data point z \in S can request to be unlearned, thus prompting the learner to modify its output model while still ensuring the same accuracy guarantees.