Extensions and Restrictions of Turing Machines

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Extensions and Restrictions of Turing Machines
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• Many extensions of Turing machines are no more
  powerful than the originals
• This is evidence that Turing machines are a
  universal model of computation
• Extensions (see this link too)
• Multiple tapes
• Multiple read write heads
• Random access
• Nondeterminism
• Two or more dimensions

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• Infinite versus semi-infinite tape
• Restricted versions of Turing Machines
• Only move to the right
• Only one state
• Never change a tape symbol
• All these restrictions make Turing machines
  weaker