Which crytocurrency was not opened on 2013/5/3?
not opened refers to open IS NULL; on 2013/5/3 refers to date = '2013-05-03'
SELECT T1.name FROM coins AS T1 INNER JOIN historical AS T2 ON T1.id = T2.coin_id WHERE T2.date = '2013-05-03' AND T2.open IS NULL