Who is the vacator for the February 1, 1971 date of successor's formal installation?
CREATE TABLE "senate" (
  "state_class" text,
  "vacator" text,
  "reason_for_change" text,
  "successor" text,
  "date_of_successor_s_formal_installation" text
);
SELECT "vacator" FROM "senate" WHERE "date_of_successor_s_formal_installation"='february 1, 1971';