The CEAF-algorithm aligns entities in key and response by means of a similarity metric, which is motivated by B 3 's shortcoming of using one entity multiple times (Luo, 2005).
although CEAF theoretically does not require to have the same number of mentions in key and response, the algorithm still cannot be directly applied to end-to-end coreference resolution systems, because the similarity metric is influenced by the number of mentions in key and response.