Let $M$ be a variant of Turing machine with no working tape but with several heads on input word. Prove that these machines accept exactly the languages in $L$.
Please hint me how to start.
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Let $S$ denote the languages accepted by such machines. The question wants you to prove $S=L$.
When you have a complicated-looking task, it often helps to break it down into pieces. So, a first helpful hint on how to break it into pieces: try to prove $S \subseteq L$. Separately, try to prove $L \subseteq S$. (If you still can't solve it, then you're able to ask a more specific question about one or the other of those.)