What is the average points of a Cosworth v8 engine in 1973.
CREATE TABLE "complete_formula_one_world_championship_" (
  "year" real,
  "entrant" text,
  "chassis" text,
  "engine" text,
  "points" real
);
SELECT AVG("points") FROM "complete_formula_one_world_championship_" WHERE "engine"='cosworth v8' AND "year"=1973;