Table: grand_prix_1971
Columns: driver
constructor
laps
time_retired
grid

Question: what is the least laps when the driver is rolf stommelen and the grid is more than 18?
SQL: SELECT MIN("laps") FROM grand_prix_1971 WHERE "driver" = 'rolf stommelen' AND "grid" > 18

Question: what is the most laps with a grid of 20?
SQL: SELECT MAX("laps") FROM grand_prix_1971 WHERE "grid" = 20