user: Question: when was the building withdrawn when the builder was ac cars and was introduced before 1958?
Columns: ['Number Range', 'Builder', 'Introduced', 'No. Built', 'Region', 'Withdrawn']
Types: ['text', 'text', 'real', 'real', 'text', 'real']
Sample row: ['79958-59', 'Bristol / Eastern Coach Works', 1958.0, 2.0, 'Scotland', 1966.0]
SQL:

assistant: SELECT "Withdrawn" FROM "Table" WHERE "Builder" = 'ac cars' AND "Introduced" < 1958.0;