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Q14

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The aim of the following question is to prove that the language {M∣M\{M \mid M is the code of the Turing Machine which, irrespective of the input, halts and outputs a\text {is the code of the Turing Machine which, irrespective of the input, halts and outputs a} 1}1\}, is undecidable. This is to be done by reducing from the language {M′,x∣M′\{M', x \mid M'  halts on \text{ halts on } x}x\}, which is known to be undecidable. In parts (a) and (b) describe the 22 main steps in the construction of MM. In part (c) describe the key property which relates the behaviour of MM on its input w to the behaviour of M′M' on xx.

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