user: Question: What is the composition with an artist of Henry Purdy, a year smaller than 2002, and a mint more than 1998?
Columns: ['Year', 'Artist', 'Composition', 'Mintage', 'Issue Price']
Types: ['real', 'text', 'text', 'real', 'text']
Sample row: [1998.0, 'Pierre Leduc', '99.999% pure gold', 1998.0, '$999.99']
SQL:

assistant: SELECT "Composition" FROM "Table" WHERE "Year" < 2002.0 AND "Mintage" > 1998.0 AND "Artist" = 'Henry Purdy';