What entrant had a Maserati 250F chassis and fewer than 6 points before 1957?
CREATE TABLE "complete_formula_one_world_championship_" (
  "year" real,
  "entrant" text,
  "chassis" text,
  "engine" text,
  "points" real
);
SELECT "entrant" FROM "complete_formula_one_world_championship_" WHERE "chassis"='maserati 250f' AND "year"<1957 AND "points"<6;