In Season 20 Episode 11, how many times was Doofus included in the credit list?
in Season 20 Episode 11 refers to episode_id = 'S20-E11'; 'Doofus' is the nickname of person; include in credit list refers to credited = 'true'
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';