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Questions tagged [decidability]

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2 answers
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Help understand why FOL wff are enumerable, but FOL is undecidable

I am very new to this. I am trying to understand some basics about what kinds of enumerations in FOL are possible, and which are not. If you accept that FOL is defined in terms of a finite number of ...
Julius Hamilton's user avatar
1 vote
2 answers
341 views

Nondeterministic Turing Machines as deciders, versus NP and co-NP

While preparing a class, I stumbled over a point that I could not elucidate. Explaining it requires a few step. Deciding vs Recognizing: A Turing machine $M$ decides a language $L$ if whenever $s\in ...
Arnaud Casteigts's user avatar
0 votes
0 answers
61 views

Undecidability of games with limited hidden state

Surprisingly, approximate win probability for one-player games with randomness and 3 bits of hidden state (in addition to non-hidden state; rational transition probabilities) is uncomputable. Question:...
Dmytro Taranovsky's user avatar
1 vote
0 answers
169 views

Decidability of the complexity of decision problems

This might be a question that is related to some of the existent questions on the topic in the title, but I still find some answers either not full, or the topic still slightly different (maybe due to ...
A. G's user avatar
  • 111
7 votes
1 answer
298 views

Is there a well-defined notion of an “R/poly” complexity class?

This would be the complexity class of all problems that are decidable in finite time with a polynomial length advice string that can be arbitrarily hard to compute. But potentially undecidable without ...
Colonizor48's user avatar
0 votes
0 answers
31 views

Decidability of Mixed-Integer Semidefinite Programs

Semidefinite programs (SDP) have an "efficient" solution, as a convex problem, by e.g. the ellipsoid method; but this comes with standard caveats as the output can be exponentially long (...
Alex Meiburg's user avatar
4 votes
1 answer
246 views

Halting problem proofs that do not utilise self-reference or diagonalization

Are there any proofs of the Halting problem that do not involve any self-reference, and diagonalization (or any diagonal argument) whatsoever? All the duplicate questions I have come across end up ...
Alan Whitteaker's user avatar
-13 votes
3 answers
1k views

Can you see that the Linz Halting Problem proof contains a fatal flaw?

Applying a Simulating Halt Decider to the Linz Halting Problem Proof When a simulating halt decider correctly simulates N steps of its input it derives the exact same N steps that a pure UTM would ...
polcott's user avatar
  • 59
7 votes
0 answers
102 views

Algorithmically determining proof complexity for Frege systems?

I apologize if this falls wildly short of research level - I am just learning the very basics of proof complexity and lack any real logic background. Let $F$ be a Frege proof system (a finite complete ...
Sprotte's user avatar
  • 171
-8 votes
1 answer
397 views

Does the Linz Ĥ applied to ⟨Ĥ⟩ correctly transition to its final reject state? [closed]

...
polcott's user avatar
  • 59
2 votes
0 answers
94 views

Tenth Hilbert problem on interval arithmetic

What is the decidability status of Hilbert's Tenth problem interpreted over interval arithmetic? In details, let $p\in\mathbb{Q}[x_1,\ldots,x_n]$ be a Diophantine polynomial. The problem is that of ...
Nicola Gigante's user avatar
3 votes
1 answer
155 views

How to solve an unification problem on $\mathbb{N}$?

Usually, the unification problem for two given terms $t$ and $s$ is to find a substitution $\theta$ such that $\theta t = \theta s$, which is equal to finding the certain $\langle x_1 , \cdots , x_n \...
Kijeong Lim's user avatar
21 votes
2 answers
1k views

Decidability of diophantine equations over {=, +, gcd}

It is well-known that polynomial diophantine equations are undecidable (Hilbert's 10th problem): that is, given a quantifier-free formula over the language $\{=, +, \cdot, 1\}$ (of equality, addition, ...
Caleb Stanford's user avatar
15 votes
1 answer
702 views

Computability and continuity

Say $L_1$ and $L_2$ are computable languages. Let $f$ be a function $L_1 \rightarrow L_2$. Let $C$ be the statement, "if $l \subseteq L_2$ and $l$ is a computable language, the preimage $f^{-1}(...
causative's user avatar
  • 255
1 vote
0 answers
30 views

Decidability of regular partition construction given its existence

Let $G = (N,T,P,S)$ be a context-free grammar where $T,N$ are sets of terminals and nonterminals respectively, $P$ contains all the productions of the grammar, and $S \in N$. If we know that $G$ is LL(...
user35443's user avatar
  • 111
3 votes
1 answer
446 views

Can the halting problem be solved probabilistically? [closed]

Let $H$ be the halting oracle, meaning that $H$ is a function on pairs of strings such that $H(P,X) = 1$ iff $P$ halts on $X$. A probabilistic program is a program that has (oracle) access to a random ...
user21820's user avatar
  • 135
3 votes
0 answers
155 views

Deciding whether an arbitrary context-free grammar generates a deterministic push-down automata?

I know that it's undecidable whether an arbitrary context-free grammar is ambiguous, but is it decidable whether that grammar is deterministic? I can't find the answer to this question anywhere on the ...
Joshua Wise's user avatar
4 votes
2 answers
276 views

Dependence of decidability on the encoding of Turing machines

Let $f : \{0, 1\}^* \to \{0, 1\}^*$ be a computable function. Given any encoding $\left<M\right>$ of Turing machines over binary (i.e., a function from the set of Turing machines to the set of ...
RandomStudent's user avatar
4 votes
1 answer
164 views

Deciding whether a 2nfa halts on every input on every branch

A 2nfa is a nondeterministic finite automaton that can move its head left or right on the input tape, or not. Is the following language known to be decidable? $$ \textit{H}_{\mathsf{2nfa}} = \{ \...
Utkan Gezer's user avatar
0 votes
0 answers
45 views

Is this a proof that diophantine equation solutions can't be bounded by power towers?

From this 2017 paper on upper bounds for solutions to diophantine equations: Conjecture 1. If a system of equations S ⊆ Bn has exactly one solution in positive integers x1, . . . , xn , then x1, ....
ghosts_in_the_code's user avatar
6 votes
1 answer
249 views

Decidability of rank-k polymorphism vs. System F

There's a paper by Kfoury from 1992, "Type Reconstruction in Finite Rank Fragments of the Second-Order $\lambda$-Calculus", that proves that type inference for Curry-style rank-$k$ polymorphic lambda ...
ionchy's user avatar
  • 325
0 votes
2 answers
239 views

Is the decidability of a language decidable? [closed]

Is there a Turing machine that takes a language as input and decides/semi-decides if it is a decidable language? Comments + answer say trivially the answer is yes; however, I'm wondering here would ...
DeeDee's user avatar
  • 301
0 votes
2 answers
225 views

Turing meta-oracle

Let H(P) be some program that given P('s source code) computes whether or not P terminates, i.e. solves the halting problem. H only needs to terminate if P terminates. (This disallows solutions like ...
Solomon Ucko's user avatar
-1 votes
1 answer
136 views

Gödel-Numbering of the Context-Sensitive Languages

I would like to have a Gödel-numbering of the context-sensitive languages. Because there is no obvious syntactic distinction between LBAs and TMs, I cannot number the former in an immediate way. So I ...
Peter Leupold's user avatar
7 votes
1 answer
432 views

Uniform mortality problem for Turing Machines

Consider the following generalisation of the mortality problem for Turing Machines. Given a Turing Machine $M$. Is there a bound $k_M$ such that starting from any configuration $c$ machine $M$ ...
Bartosz Bednarczyk's user avatar
9 votes
1 answer
524 views

Is there an algorithm that finds the forbidden minors?

The Robertson–Seymour theorem says that any minor-closed family $\mathcal G$ of graphs can be characterized by finitely many forbidden minors. Is there an algorithm that for an input $\mathcal G$ ...
domotorp's user avatar
  • 14k
5 votes
1 answer
231 views

Post correspondence problem for finite monoids

The Post correspondence problem has the following version for finite monoids: Input: a finite monoid $M$ and a finite list $(m_1,m_1'),\ldots, (m_n,m_n')$ of pairs of elements of $M$ Question: is ...
user23902's user avatar
2 votes
1 answer
330 views

Petri net termination

Termination is the following problem. Input: a Petri Net with initial marking Output: "yes" iff there exists an infinite firing sequence. The naive algorithm in the case of bounded nets for example ...
Alberto's user avatar
  • 191
2 votes
2 answers
211 views

How can you state how abstract interpretation gets around Rice's Theorem succinctly?

At this question, abstract interpretation has a nice in-depth look. However, I'd like someone to clearly and very precisely state how abstract interpretation takes the result of Rice's Theorem over ...
CinchBlue's user avatar
  • 309
4 votes
2 answers
1k views

Enumerating decidable languages

[The assumption in this question is wrong. It is possible to enumerate exactly the decidable languages with semideciders.] Lets say we have a TM $M_E$ enumerator that writes out codes of TM's on a ...
sixpanbass's user avatar
6 votes
1 answer
2k views

Show that minimal CFG is undecidable via mapping reduction

Actually the problem below is an exercise in Sipser's textbook (Problem 5.36). However, from my perspective, it is not so trivial so that I post this question on this site instead of CS.SE. The ...
Lwins's user avatar
  • 395
1 vote
0 answers
100 views

Deciding reachability under iterated independent polynomial mapping

For any $1\leq i\leq m$, $f_i: \mathbb{Q}\rightarrow \mathbb{Q}$ is a polynomial mapping over $x_i$, where $\mathbb{Q}$ is the set of rationals. For $\vec{a}_0=(a_1, \cdots, a_m)\in \mathbb{Q}^m$, we ...
Liam_math's user avatar
0 votes
1 answer
200 views

Is Buchberger's algorithm or Wu's method valuable theoretically when we have the Tarski–Seidenberg theorem?

Is Buchberger's algorithm or Wu's method valuable theoretically when we have the Tarski–Seidenberg theorem? In other words, could the Tarski–Seidenberg theorem subsume Buchberger's algorithm and Wu's ...
XL _At_Here_There's user avatar
19 votes
1 answer
1k views

Is equivalence of unambiguous context-free languages decidable?

It is well known that the equivalence problem is undecidable for general context-free languages. However, all proofs of this fact that I am aware of seem to involve some ambiguous context-free ...
Jára Cimrman's user avatar
5 votes
0 answers
96 views

Which computational models support bigotous programs?

A bigotous program is a program which decides if its input is semantically equivalent to itself. Of course, this is impossible in a Turing complete language due to Rice's theorem. In fact, its pretty ...
Christopher King's user avatar
4 votes
2 answers
624 views

About the decidability of sets enumerated in non decreasing order

It is well known that a set of numbers enumerable in nondecreasing order is decidable. However, the typical proof, by cases on the finiteness of the enumerated set, is not constructive. In general, it ...
Andrea Asperti's user avatar
5 votes
1 answer
537 views

Proof that the theory of rationals is convex

In Example 10.12 of the book The calculus of computation by Bradley and Manna, it is said The theory of rationals is convex, as it is convex in a geometric sense. How does the geometric sense of ...
np20's user avatar
  • 153
6 votes
1 answer
326 views

Proof of decidability of type checking of calculus of (co)inductive constructions?

I often see it asserted that type checking is decidable for CIC, but I haven't seen it proven. Is there a good paper (or simple demonstration) of this?
Shea Levy's user avatar
  • 213
18 votes
2 answers
883 views

Deciding whether a unary context-sensitive language is regular

It is a well-known result that the question Does a context-free grammar generate a regular language? is undecidable. However, it becomes decidable on a unary alphabet, simply because in this case,...
J.-E. Pin's user avatar
  • 4,831
35 votes
3 answers
3k views

Turing Machine restrictions that render halting decidable

If one restricts Turing Machines to a finite tape (i.e., to use bounded space $S$), then the halting problem is decidable, essentially because after a number of steps (which can be calculated from the ...
Joseph O'Rourke's user avatar
8 votes
0 answers
415 views

Decidability of existential first-order theory of reals with exponential

The first-order theory over the reals as an ordered field with polynomials is decidable with doubly exponential complexity. However, if we additionally allow the exponential function, that is $e^x$ ...
Heinrich Ody's user avatar
-1 votes
1 answer
147 views

Global satisfiability in LTL

In propositional linear temporal logic (LTL) over $\mathbb{N}$, it is decidable whether a formula $\varphi$ is satisfiable from time point 0. Is it known to be un/decidable to check the ...
Tyler Durden's user avatar
0 votes
2 answers
332 views

Are there any open problems concerning decidability? [duplicate]

I am learning computability theory. I am just interested to know some famous problems (Formally languages) whose decidability is in question.
Saravanan's user avatar
  • 119
9 votes
1 answer
239 views

Oracle-Decidability of Algebraic Independence

Consider numbers $x_1,...,x_n\in \mathbb{R}$ given by TMs $M_1,...,M_n$ such that $M_i$ approximates $x_i$ to an arbitrary precision (by allowing it to run longer and longer). I am interested in the ...
Shaull's user avatar
  • 5,646
6 votes
2 answers
278 views

FSM transducer sequential composition decidability

this is a followup/ sequel to this recent question which was answered, this one presumably significantly harder. consider a deterministic FSM transducer $F$ and its mapping $F(x)$ of an input word $x$....
vzn's user avatar
  • 11k
25 votes
2 answers
2k views

Is it decidable to determine if a given shape can tile the plane?

I know that it is undecidable to determine if a set of tiles can tile the plane, a result of Berger using Wang tiles. My question is whether it is also known to be undecidable to determine if a single ...
Joseph O'Rourke's user avatar
5 votes
1 answer
236 views

Is algebraic dependency decidable?

A set of numbers $S=\{x_1,...,x_n\}$ is said to be algebraically dependent if there exists a (multivariate) polynomial $p$ with coefficients in $\mathbb Q$ whose roots contain $x_1,...,x_n$ (or a ...
Shaull's user avatar
  • 5,646
3 votes
1 answer
4k views

Deciding whether a context-free language is regular [closed]

Does anyone know whether the following decision problem is decidable: Given a context-free language $L$, is $L$ regular? Here $L$ can be expressed, e.g., using a context-free grammar. Does anyone ...
Petar Tsankov's user avatar
2 votes
0 answers
871 views

Decidability of CFG ambiguity

I have been trying to show the following language is undecidable. $L = \{ (\langle G \rangle , n ): G$ is a context-free grammar with an ambiguous string of length $\le n \}$. I think it is ...
Kuhndog's user avatar
  • 233
12 votes
2 answers
286 views

Vector Addition Systems with finite "obstacles"

A Vector Addition System (VAS) is a finite set of actions $A \subset \mathbb{Z}^d$. $\mathbb{N}^d$ is the set of markings. A run is a non-empty word of markings $m_0 m_1\dots m_n$ s.t. $\forall i \in \...
Nicolas Perrin's user avatar