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I am looking at the following:
Costruct a composite turing machine, that reverses the words $w_1$ and $w_2$ over the alphabet $\{\_, x_2, \ldots , x_m\}$ as follows:
$$\ldots \_ w_1\_ w_2\underline{\_} \ldots \mapsto \ldots \_ w_2^R\_ w_1\underline{\_} \ldots$$
The first symbol of $w_2^R$ is ...
