CREATE TABLE table_13237 ("Position" TEXT, "Player" TEXT, "Loaned to" TEXT, "Date" TEXT, "Loan expires" TEXT)

What date has a loan expires date of end of the season, and a Position of mf?
SELECT "Date" FROM table_13237 WHERE "Loan expires" = 'end of the season' AND "Position" = 'mf'
SELECT "Date" FROM "table_13237" WHERE "Loan expires" = 'end of the season' AND "Position" = 'mf'