Who is the opponent in the final when frankfurt is championship and the year is less than 1993.0?
CREATE TABLE "singles_6_5_titles_1_runner_up" (
  "outcome" text,
  "year" real,
  "championship" text,
  "surface" text,
  "opponent_in_the_final" text,
  "score_in_the_final" text
);
SELECT "opponent_in_the_final" FROM "singles_6_5_titles_1_runner_up" WHERE "championship"='Frankfurt' AND "year"<1993.0;