Name the partner for surface of grass and opponents of jürgen melzer philipp petzschner
CREATE TABLE "doubles_29_16_titles_13_runners_up" (
  "outcome" text,
  "date" text,
  "surface" text,
  "partner" text,
  "opponents_in_the_final" text,
  "score_in_the_final" text
);
SELECT "partner" FROM "doubles_29_16_titles_13_runners_up" WHERE "surface"='grass' AND "opponents_in_the_final"='jürgen melzer philipp petzschner';