Sentence distance between the potential antecedent and anaphor; c. Syntactic tag of them, whether they are leaf node or not in the parsing tree; d. Syntactic tag bi-grams of them, and whether their syntactic tags are identical; e. Named entity tags of them, bi-gram of these tags, and whether they are identical; f. Syntactic tag path to root of them, bi-gram of these paths, and whether they are identical; g. Whether they are predicates; h. Features of anaphor: Its head predicates and types, words, pos tags, the words and pos tags of the left/right 3 neighbor tokens, and bigrams; i.
we consider mentions that correspond to a word or an internal node in a syntactic tree and ignore the rest mentions, as we think a mention should be a valid meaningful unit of a sentence.