CREATE TABLE table_50813 ("Edition" TEXT, "Round" TEXT, "Date" TEXT, "Against" TEXT, "Surface" TEXT, "Opponent" TEXT, "Result" TEXT)

what is the date when the surface is clay and the result is 6 7 (4 7) , 1 6?
SELECT "Date" FROM table_50813 WHERE "Surface" = 'clay' AND "Result" = '6–7 (4–7) , 1–6'
SELECT "Date" FROM "table_50813" WHERE "Result" = '6–7 (4–7) , 1–6' AND "Surface" = 'clay'