user: Question: When did the Theme of Bobsleigh release?
Columns: ['Date of Issue', 'Theme', 'Denomination', 'Printer', 'Quantity', 'Design', 'Perforation', 'First Day Cover Cancellation']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['7 February 1992', 'Ski Jumping', '42 cents', 'Ashton-Potter Limited', '3 000 000', 'Designed by Peter Adam and Katalin Kovats', '12.5 x 13', 'N/A']
SQL:

assistant: SELECT "Date of Issue" FROM "Table" WHERE "Theme" = 'Bobsleigh';