Who was the runner-up, when the champion was Björn Borg after 1978?
CREATE TABLE "singles_champions" (
  "location" text,
  "year" real,
  "champion" text,
  "runner_up" text,
  "score" text
);
SELECT "runner_up" FROM "singles_champions" WHERE "champion"='björn borg' AND "year">1978;