Decidable languages are languages such that the problem of whether a given word belongs to it or not is decidable. A decision problem, i.e., a question with a yes/no answer, is called decidable if there exists an algorithm (a Turing machine) that can and will return a Boolean true or false value (instead of looping indefinitely).
Questions tagged [decidable]
92 questions
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Is the language {⟨A⟩∣A is an NFA and L(A)={0,1}∗} decidable? decidable?
How would one go about proving/disproving the language {⟨A⟩∣A is an NFA and L(A)={0,1}∗}
is/isn't decidable?
I assumed at first since it was an NFA involved it would be decidable, but since there is no input string to simulate does this change…
AceVenturos
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Turing machine decidability ambiguous cases
1) Is a Turing machine M that accepts the language L = {ε}, accepting no entry?
In one hand, I think it can be false because the empty word could be an entry, but in another i think this could possibly be an indecidable problem.
2) Is every Turing…
Cmôn
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Given the encoding of a specific Turing machine, can it be decided if it will halt on a specific input?
Say I have the Universal Turing Machine encoding of a specific Turing machine T. Also say I have the encoding of a specific input s. Is the question of whether T halts on s decidable? Can simulating running T on s be used to reach an answer?
helloJoe
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Check whether 2 languages are Turing recognizable or co-Turing recognizable
I have these 2 languages
A = { | M is a TM and L(M) contains exactly n strings }
B = { | N is a TM and L(N) contains more than n strings }
I believe that these 2 are undecidable, but I am not sure whether they are Turing recognizable or…
PTN
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Can we decide if a number n belongs to a countable set S?
The question at hand is the following:
Let S be a subset of N (natural numbers), so it is infinite and countable. Let Ls={a^n | n belongs to S} a language. Is Ls recursive? Is Ls recursively enumerable? Justify your answers.
I'm pretty sure that Ls…
andreasgtech
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Show that the language is decidable
How do I show this language
{ | C,A,B are DFAs, L(C) contains the shuffle of L(A) and L(B)}
is decidable ?
I believe if I can construct automatas for A and B, then I can get an automata that contains the shuffle of them.
I am also thinking…
PTN
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Turing Machines and Machine Schemas
Arthur Dent, using space age technology not yet available on earth developed an algorithm which determines if a TM M1 halts or not when started on a blank tape. But then later, he discovered that the meaning to life, the universe, and everything is…
Bobby S
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Have a decider decides {|M is TM and |L(M)|=n}, build a decider decides n-1
Is this possible?
Suppose that we have a decider decides {|M is a TM and |L(M)|=n}
Want to build a decider decides {|M is a TM and |L(M)|=n-1}
If possible, how?
Patroclus
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How Arbitrary is the Representation of a Turing Machine?
I'm working on a related decidability/recognizable problem, and to solve it, I need clarification about the encoding/representation of a turing machine.
I know a turing machine is formally defined as a 7-tuple. If I have a Turing Machine U and…
prelic
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what is exactly the halting in turing machines ?
I am new to decidability. I read halting problem of halting problem but didn't get anything what it is actually implying. I am already screwed up with the explaination.
Can anyone provide me any sound explaination or atleast some details, it would…
Garrick
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Proving that a language's length is divided by 2 is undecidable
How can I prove using a reduction method that a language's length is divided by 2?
L={ | is a Turing machine where |L(M)|= 0 mod 2}
I have 2 ideas but I am afraid to follow the wrong one
1) I use the reduction method with Amt and I say that the…
Zok
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Direct Reduction, Turing machine and a DFA
I have been reading and I am trying to understand the reduction when it comes to truing machine. This is how I understand it: it means that it reduces problem A into problem C. But I am not quite sure how it totally works.
lets see an example:
Given…
David
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P is undecidable and not semidecidable, Q is undecidable and semidecidable and P ⊂ Q
My problem: Define two sets P and Q of words (that is, two problems) such that:
P is undecidable and not semidecidable, Q is undecidable and semidecidable and P ⊂ Q
Lorenzo J Serranti
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NP and 3-SAT and One Facts
any expert could help me why this sentence is True?
if L ∈ NP and L ≤p 3−SAT (i.e: reduce L to 3-SAT in poly time) then L is NP-Complete.
user4554402
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Complete System for Creating Unambiguous Grammars
I'm in an undergraduate class where we're studying formal grammars right now. I asked my teacher if there was any known set of rules for creating context free grammars that
1) Was guaranteed to produce an unambiguous grammar.
2) Allows for the…
sync
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