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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How to prove that the language $E_{tm}$ is $NP-Hard$
Consider the language $E_{tm}={ \langle M \rangle: M\text{is a Turing Machine that accepts nothing}$
I am not sure how to even start.
My idea is to provide poly time reduction from some NP - Complete problem.
E_tm
What I don't understand is that,…
acagu
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Prove that a specific language is not semidecidable
I have to prove that the language L = {< M >: |L(M)| <= 2016} is NOT semi-decidable. Now I thought of doing it like this:
Take a random alfabet E. Now there are an infinite number of words in E. We can only conclude that |L(M)| <= 2016 by passing…
user4424299
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Turing Machine for regular languages
Theorem 5.3 from Sipser's TOC book is about decidability of Regular_TM = {M | M is a Turing Machines (TMs) and L(M) is regular languages}. For the sake of reaching a contradiction, TM R is assumed to be a decider for Regular_TM and then R is used to…
Mba7eth
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decidable languages (Computational Models)
I need to prove whether L is decidable or not:
L={ | M is a TM and the union of L(M) and H_TM is in RE}
( H_TM={ | M is a TM that halts on w} )
ChikChak
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Prove whether this language is decidable or undecidable
So I am reviewing my notes for this problem, and I cant seem to understand how this problem works. Say we have M, and M accepts an input that makes it visit every non-halting state.
I convinced myself that this problem is decidable, but I am having…
user4077377
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Cannot create algorithm for decidable language
L2 = { : M is a TM and there exists an input string w such that M halts within 10 steps on input w}
Hi. I am creating an algorithm to show above L2 is decidable.
And the hint is given as following:
To show L2 is decidable, test given TM M on…
Ryu Hoshi
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Z3 reports "unknown" for some formulas involving (_ as-array ...)
Z3 (version 4.4.1) reports "unknown" for many of the queries generated by a tool I'm writing, and I've narrowed the problem down to the use of (_ as-array ...):
(declare-sort MyType)
(declare-fun f (MyType) Bool)
(declare-const a1 (Array MyType…
Calvin
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How to prove a string is decidable (formal languages)
I am trying to prove if string in machine L(M) is decidable and i am not able to find appropriate results for that. could anyone help me in explaining some example on this.
The scenario that I am trying is I have a two strings and S1 is a subset of…
Deepak
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Parameterizing a proposition over other parameterized propositions of unknown arity in Coq
I want to define a parameterized proposition decidable that talks about the decidability
of other parameterized propositions. To take a common example, even is a parameterized proposition that takes 1 parameter of type nat, and it is decidable. lt…
user287393
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How to come up with a solution of finite or infinite language using context free grammar?
I am trying to come up with a solution of finite or infinite language using context free grammar.
I have these grammars to find if it's a solution of finite or infinite language
S -> XY|bb Step 1
X -> XY|SS Step 2
Y -> XY|SS Step 3
So I would…
Ris
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natural numbers and the difference between recognizable and decidable?
I found the following explanation from Math exchange
A language is Recognizable iff there is a Turing Machine which will halt and accept only the strings in that language and for strings not in the language, the TM either rejects, or does not halt…
user3277633
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Wonder is the following language finite
There is a question about the following language is finite or not in my class
{w : w is a regular expression for {ambn:m+n≤k}} where k is a specific natural number.
I think it is finite, because there can be at most (K+1)*k/2 words in the…
Ghostblade
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Every regular language is decidable
I am a trying to prove that every regular language is decidable.
So in order to prove that I am trying to show that I can move from deterministic finite automaton (DFA) to a Turing decidable machine.
So I am not sure how to construct a Turing…
Ohad
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L = {T | T is a turing machine that recognizes {00, 01}} Prove L is undecidable
L = { | T is a turing machine that recognizes {00, 01}}
Prove L is undecidable.
I am really having difficulties even understanding the reduction to use here.
I'm not asking for free lunch, just a push in the right direction.
user1405177
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Turing machines and decidability
It is known that there are decidable problems, semi-decidable problems, and undecidable problems. A language that is accepted by a TM (Turing Machine) is a r.e. set (recursively enumerable), and, in some cases, a recursive set as well. An example of…
jbushi
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