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the rest to build the full distance matrix. 226 

## 3.3. The PAN Benchmark Dataset 

227 

We tested our algorithm on datasets from the two most recent PAN CLEF 228 (2013) competitions, which provide benchmark datasets for authorship attri- 229 bution. From PAN 2013 we selected the author identification task described 230 in Juola and Stamatatos (2013). In this task 349 training texts are provided, 231 divided in 85 problems out of which 30 are in English, 30 in Greek and 25 232 in Spanish. For each set of documents written by a single author it must be 233 determined if a questioned document was written by the same author or not. 234 Each text is approximately 1000 words long, which is close to our empirical 235 

