Let L = {M: M is a Turing machine that accepts at least two binary strings}.

a) De?ne the notions of Turing-recognisable language and undecidable language.

b) Is L Turing-recognisable? Justify your answer with an informal argument.

c) Justify with a formal proof your answer to b). [10 marks] d) Prove that L is undecidable. (Hint: use Rices theorem.)