Database: simpson_episodes
Question: In Season 20 Episode 11, how many times was Doofus included in the credit list?
SQL: SELECT COUNT(*) FROM Person AS T1 INNER JOIN Credit AS T2 ON T1.name = T2.person WHERE T1.nickname = 'Doofus' AND T2.credited = 'true' AND T2.episode_id = 'S20-E11';