What was the name of the opponent when the method was ko (slam), and record was 13–1?
CREATE TABLE "mixed_martial_arts_record" (
  "res" text,
  "record" text,
  "opponent" text,
  "method" text,
  "event" text,
  "round" real,
  "time" text,
  "location" text
);
SELECT "opponent" FROM "mixed_martial_arts_record" WHERE "method"='ko (slam)' AND "record"='13–1';