Question: Calculate the percentage of words used in Agents class label.
SQL: SELECT CAST(COUNT(DISTINCT CASE WHEN T1.class_label = 'Agents' THEN T2.word_cited_id ELSE NULL END) AS REAL) * 100 / COUNT(DISTINCT T2.word_cited_id) FROM paper AS T1 INNER JOIN content AS T2 ON T1.paper_id = T2.paper_id