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I'm fairly new to Turing Machines and I'm stumped on a question. I'm given a Turing machine: M = (Q,Σ,Γ,δ,q) such that Q={q,r,s,t}, Σ={a.b.c}, Γ={B,a,b,c} and δ is defined by the following: [q,a,r,b,R], [q,b,r,a,R], q,c,t,c,R], [t,a,t,a,R], [t,b,t,b,R], [t,B,s,B,R]

And I'm asked if M halts on the input abba, and if so write the configuration in which M halts. The answer is suppose to be brbba, which I don't understand how this can be the configuration. How does a state symbol become apart of the configuration? Any help will be appreciated!

1 Answers1

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A configuration consists of:

  • the current state
  • the position of the read/write head
  • the tape content

brbba indicates all three as the r shows the current state and the head's position. A less compact way to write it in two lines would be:

 r
bbba

or b[rb]ba if you like.

Peter Leupold
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