Please prove both ways

Problem 50. Prove: A language A C 10, 1)* is co-c.e. if and only if there is a decidable language B C 10,1 such that, for all e 10,1 Problem 50. Prove: A language A C 10, 1)* is co-c.e. if and only if there is a decidable language B C 10,1 such that, for all e 10,1