To verify our assumption that PreCo embodies the core challenges of coreference, we evaluate a strong baseline coreference resolver on it.
we (i) estimate the room for improvement of the baseline system to show that the dataset is challenging, (ii) study the impact of training-test overlap to model performance and error analysis to show the advantages of PreCo, and (iii) quan-  titatively evaluate the mention detector to understand the bottlenecks of the coreference resolution system.