CREATE TABLE table_57543 ("Driver" TEXT, "Constructor" TEXT, "Laps" FLOAT, "Time/Retired" TEXT, "Grid" FLOAT)

Which constructor had a Time/Retired of collision, where the grid number was less than 18 and Nick Heidfeld was the driver?
SELECT "Constructor" FROM table_57543 WHERE "Time/Retired" = 'collision' AND "Grid" < '18' AND "Driver" = 'nick heidfeld'
SELECT "Constructor" FROM "table_57543" WHERE "Driver" = 'nick heidfeld' AND "Grid" < '18' AND "Time/Retired" = 'collision'