Which Men's singles has a Mixed doubles of kai abraham petra michalowsky?
CREATE TABLE "previous_winners" (
  "year" text,
  "men_s_singles" text,
  "men_s_doubles" text,
  "women_s_doubles" text,
  "mixed_doubles" text
);
SELECT "men_s_singles" FROM "previous_winners" WHERE "mixed_doubles"='kai abraham petra michalowsky';