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Decidability Problems for Grammars
Some Reduction Inferences
Example reductions
Recent questions tagged decidability
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Hopcroft, Ullman Theorem 9.7 Reductions
There exists a language Ld = {M | M doesn't belong to L(M)}. Ld is the collection of Turing machines (programs) M such that M does not halt and accept when given itself as input. It is known and proved that Ld is a non-Recursively ... and Ld is non-RE, ATM must be non-RE. But we know that ATM is Recursively Enumerable and undecidable. How is this possible?
dopq12
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Theory of Computation
Mar 5
by
dopq12
58
views
decidability
theory-of-computation
turing-machine
reduction
recursive-and-recursively-enumerable-languages
4
votes
0
answers
2
GO Classes Test Series 2024 | Mock GATE | Test 14 | Question: 65
Which of the following statements are true for every language $\mathrm{L} \subseteq\{0,1\}^*?$ $L^{\star}$ is infinite. $L$ is accepted by some DFA if and only if $L$ is accepted by some NFA. If $\mathrm{L}$ is the ... $\mathrm{L}$ is undecidable. If $\mathrm{L}$ is the union of two decidable languages, then $\mathrm{L}$ is decidable.
GO Classes
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in
Theory of Computation
Feb 5
by
GO Classes
548
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goclasses2024-mockgate-14
theory-of-computation
decidability
multiple-selects
2-marks
3
votes
1
answer
3
GO Classes Test Series 2024 | Mock GATE | Test 11 | Question: 61
Which of the following is/are undecidable? $L=\left\{\langle M\rangle \mid M\right.$ is a TM, $\mathrm{L}(M) \neq \emptyset$, and $\left.\mathrm{L}(M) \neq \Sigma^*\right\}$. $\{\langle M\rangle \mid M$ ... $\}$ $L=\{\langle M\rangle \mid M$ is a DFA and $L(M)$ is uncountable $\}$
GO Classes
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in
Theory of Computation
Jan 13
by
GO Classes
526
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goclasses2024-mockgate-11
goclasses
theory-of-computation
decidability
multiple-selects
2-marks
1
vote
0
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Decidability
L(M)={0} We can have Tyes for {0} and Tno for Σ∗ ({0}⊂Σ∗{0}⊂Σ∗). Hence, L={M ∣ L(M)={0}} is not Turing recognizable (not recursively enumerable) I don’t understand why this is not decidable. We can easily create a turing that accepts this language
amitarp818
asked
in
Theory of Computation
Dec 28, 2023
by
amitarp818
216
views
decidability
theory-of-computation
turing-machine
recursive-and-recursively-enumerable-languages
0
votes
0
answers
5
Undecidability Doubt
If G is a CFG then L(G) = (Sigma)* is Decidable or Undecidable? The reference where I solved this question says this is an Undecidable problem! But I think it's Decidable . Help would be appreciated.
Sparsh-NJ
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in
Theory of Computation
Aug 6, 2023
by
Sparsh-NJ
215
views
theory-of-computation
decidability
0
votes
1
answer
6
#gate questions
which one true 1. Determining whether context-free grammar is un-decidable 2. Whether a given grammar is context-free is decidable
amit166
asked
in
Theory of Computation
Jan 29, 2023
by
amit166
333
views
decidability
1
vote
0
answers
7
DRDO CSE 2022 Paper 2 | Question: 12 (a)
Let $L_{1}$ and $L_{2}$ be two languages decidable by Non-deterministic Turing machines $M_{1}$ and $M_{2}$. Using $M_{1}$ and $M_{2}$, construct a Non-deterministic Turing machine for the following languages. $L_{1} \cup L_{2}$
admin
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in
Theory of Computation
Dec 15, 2022
by
admin
278
views
drdocse-2022-paper2
theory-of-computation
decidability
turing-machine
2-marks
descriptive
2
votes
0
answers
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DRDO CSE 2022 Paper 2 | Question: 13
Let $L$ be the following language. $L=\left\{P\left(x_{1}, x_{2}, \ldots, x_{n}\right) \mid P\right.$ is a polynomial with an integral root $\}$. Explain why the following Turing Machine description cannot decide the language $L$. ... $0,$ accept. Else, reject.
admin
asked
in
Theory of Computation
Dec 15, 2022
by
admin
230
views
drdocse-2022-paper2
theory-of-computation
decidability
turing-machine
4-marks
1
vote
0
answers
9
DRDO CSE 2022 Paper 2 | Question: 12 (b)
Let $L_{1}$ and $L_{2}$ be two languages decidable by Non-deterministic Turing machines $M_{1}$ and $M_{2}$. Using $M_{1}$ and $M_{2}$, construct a Non-deterministic Turing machine for the following languages. $L=\left\{a \circ b \mid a \in L_{1}, b \in L_{2}\right\}$ where $a$ o $b$ denotes the concatenation of the strings $a$ and $b$
admin
asked
in
Theory of Computation
Dec 15, 2022
by
admin
181
views
drdocse-2022-paper2
theory-of-computation
decidability
turing-machine
2-marks
descriptive
1
vote
0
answers
10
DRDO CSE 2022 Paper 2 | Question: 12 (c)
Let $L_{1}$ and $L_{2}$ be two languages decidable by Non-deterministic Turing machines $M_{1}$ and $M_{2}$. Using $M_{1}$ and $M_{2}$, construct a Non-deterministic Turing machine for the following languages. $L_{1} \cap L_{2}$
admin
asked
in
Theory of Computation
Dec 15, 2022
by
admin
259
views
drdocse-2022-paper2
theory-of-computation
decidability
turing-machine
2-marks
descriptive
1
vote
2
answers
11
toc decidablity
M is a Turing Machine and M is the only Turing Machine that accepts L(M) is decidable. TRUE/FALSE
jugnu1337
asked
in
Theory of Computation
Nov 8, 2022
by
jugnu1337
612
views
theory-of-computation
decidability
true-false
4
votes
1
answer
12
GO Classes Test Series 2023 | Theory of Computation | Test 5 | Question: 4
Consider the following languages : $\mathrm{L} 1:=\{\langle \text{M}\rangle \mid \text{M}$ is a $\text{TM},$ and $\text{M}$ is the only $\text{TM}$ that accepts $\mathrm{L}(\mathrm{M})\}.$ ... and $|\text{M}|<1000\} .$ Which of the above languages is Decidable? Only $\text{L1}$ Only $\text{L2}$ Both None
GO Classes
asked
in
Theory of Computation
Aug 1, 2022
by
GO Classes
591
views
goclasses2024-toc-5-weekly-quiz
goclasses
theory-of-computation
turing-machine
decidability
1-mark
1
vote
1
answer
13
Igate Test Series
please explain all options with example
SKMAKM
asked
in
Theory of Computation
Jul 20, 2022
by
SKMAKM
553
views
decidability
closure-property
0
votes
1
answer
14
MADE EASY 2022 Work book -Theory of Computation series
Let L be a regular language on alphabet Σ. The union of the myhill-nerode equivalence classes is always _____, and the pairwise intersection of the myhill-nerode equivalence classes is always Fill up the blanks
abhinowKatore
asked
in
Theory of Computation
Mar 7, 2022
by
abhinowKatore
387
views
theory-of-computation
regular-languages
finite-automata
minimal-state-automata
decidability
12
votes
2
answers
15
GATE CSE 2022 | Question: 36
Which of the following is/are undecidable? Given two Turing machines $\textit{M}_{1}$ and $\textit{M}_{2},$ decide if $\textit{L(M}_{1}) = \textit{L(M}_{2}).$ Given a Turing machine $\textit{M},$ decide if $\textit{L(M)}$ is ... $\textit{M},$ decide if $\textit{M}$ takes more than $1073$ steps on every string.
Arjun
asked
in
Theory of Computation
Feb 15, 2022
by
Arjun
9.8k
views
gatecse-2022
theory-of-computation
turing-machine
decidability
multiple-selects
2-marks
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