user: Question:  what's the notes where withdrawn is 1956–57
Columns: ['Number Range', 'Introduced', 'Builder', 'Engine', 'Weight (long tons)', 'Seats', 'Withdrawn', 'Notes']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['1', '1934', 'Park Royal', '1 AEC of hp (kW)', 'long tons (t; short tons)', '69', '1955', 'Prototype railcar']
SQL:

assistant: SELECT "Notes" FROM "Table" WHERE "Withdrawn" = '1956–57';