Transcript Extensions and Restrictions of Turing Machines • Many extensions of Turing machines are no more powerful than the originals • This is evidence.

Extensions and Restrictions of
Turing Machines
• 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)
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Multiple tapes
Multiple read write heads
Random access
Nondeterminism
Two or more dimensions
– 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