user: Question: who wrote the episode "He Ain't Heavy"?
Columns: ['Series #', 'Season #', 'Title', 'Written by', 'Original air date', 'U.S. Viewers (millions)']
Types: ['real', 'real', 'text', 'text', 'text', 'text']
Sample row: [46.0, 1.0, '"A Decent Proposal"', 'Kari Lizer & Jeff Astrof', 'September24,2008', '6.52']
SQL:

assistant: SELECT "Written by" FROM "Table" WHERE "Title" = '"He Ain''t Heavy"';