Questions tagged [proofs]

Used for questions about existing or possible proofs of a specific theorem or conjecture

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2 answers
33 views

Combining different length epsilon-ADU hash function families

For context, an $\epsilon$-almost delta universal ($\epsilon$-ADU) hash function family $\mathcal{H} = \{h : M \to D\}$ hashes inputs from $M$ to digests in $D$ such that for any distinct $m, m' \in M$...
5 votes
0 answers
250 views

What's wrong with this $P \neq BPP$ proof?

I developed this simple argument while learning about the $BP$ operator and McCreight and Meyer's Union Theorem, however I cannot pinpoint where my error is. By the Union Theorem, there exists a total ...
-4 votes
1 answer
146 views

If I want to end math, where should I start?

I'm a PhD in math, but I'm not good. I'm familiar with Riemannian geometry, a little partial differential equations, and a little algebraic topology. And the other undergraduate courses of math (I ...
2 votes
0 answers
48 views

Is this variant of Facilities location problem a NP-hard problem?

Given a set of locations $P=\{p_1,p_2,\dots\}$ and a set of facilities $F=\{f_1,f_2,\dots\},|F|\ge k$ on a plane. We want to partition the facilities into $k$ disjoint subsets (each subset has at ...
0 votes
0 answers
46 views

Proving the Equivalence of REGEX r^n and r^{..n} when r Is Nullable

Im seeking clarification and a rigorous proof regarding the equivalence of r^n and r^{..n} in the context of formal languages, particularly when r is nullable. To clarify the terminology: r denotes ...
1 vote
0 answers
36 views

Overlap operator for simple ( regex-like ) Patterns

( Introduction ) Some Notation lower case letters, $a, b, c$ will be used to denote single symbols Upper case letters, $P, Q, R$ will be used to denote string of symbols $a\!:\!S$ means a string ...
7 votes
1 answer
157 views

Conversion between NP certificates

This might be a well-known fact, but I can't convince myself of whether this is true. Suppose I have some NP language and two different verifying procedures V and V' for L. For any x in L, is it the ...
3 votes
0 answers
66 views

What's the difference between "modular" and "compositional"?

When talking about reducing complexity in a software system, we often talk about making it "modular" by breaking it up into multiple modules that are all linked together to form the overall ...
29 votes
4 answers
5k views

Implications of unprovability of $P\neq NP$

I was reading "Is P Versus NP Formally Independent?" but I got puzzled. It is widely believed in complexity theory that $\mathsf{P} \neq \mathsf{NP}$. My question is about what if this is ...
4 votes
1 answer
221 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 ...
0 votes
1 answer
145 views

Sources that prove solving 2-SAT with DP takes linear time

Would anyone have any sources that describe/an explanation of how solving 2-SAT using dynamic programming takes a linear amount of time? Can't seem to find a text that proves it in detail/formality. ...
1 vote
1 answer
209 views

Uniqueness of the distribution maximizing the channel capacity

Setting: We look at a discrete memoryless channel which takes an input probability distribution acting over symbols in $\mathcal{X}$ to an output probability distribution over symbols in $\mathcal{Y}$....
0 votes
1 answer
116 views

On the proof of $PP = P \iff \#P = FP$ in Arora & Barak (Lemma 17.7)

Introduction I am currently studying chapter 17 (of the famous textbook by Arora & Barak [1]) on the complexity of counting and got stuck on the proof of Lemma 17.7, which states $\mathrm{PP} = \...
5 votes
1 answer
170 views

Establishing competing memory limits for pushdown automata

Let $L$ be the language of all even-length strings whose first half is a palindrome. Let $L$ be the language of all even length strings whose first half is imbalanced—with an unequal number of $\...
0 votes
0 answers
68 views

A fundamental question about the proof by induction in session types

I have a question about proof by induction in the domain of session types. Let's assume we have the following lemma: $$ \text{Let}~ \Gamma \vdash P : T. ~~\text{If } P = \mu X. Q ~~\text{then}~~ \...
8 votes
1 answer
138 views

Construction of arbitrary functions with exponential-size $MODp \circ MODq$ circuits

It is mentioned in multiple papers [1], [2] that $MODp \circ MODq$ circuits for two distinct primes $p, q$ can compute arbitrary functions in exponential size. However, [1] provides no citation for ...
4 votes
0 answers
180 views

Any problems for which we know the complexity, but no algorithms with the same time?

I suddenly found myself wondering if there are any problems for which the complexity (time or space or anything else) is proven, say to be O(n^2), but for which the best known algorithms are worse ...
4 votes
2 answers
116 views

Proving that a given formula in LTL is the smallest way to express it

I am looking for a way to prove that a given LTL formula is expressed with the fewest number of temporal operators possible. I would like to do this to compare the expressive length with other ...
3 votes
1 answer
367 views

How hard is this combinatorial optimisation problem?

Suppose we have multiple intervals $R_1,R_2,...,R_i$ of non-negative integers. These intervals may overlap and we use $R_h(\mathrm{median})$ to denote the median integer in the $h$-th interval $R_h$, ...
4 votes
3 answers
419 views

Proving proof system properties within the proof system itself?

While reading about Frege proof systems in [1], I came across the completeness theorem and its proof, which involves a few lemmas introduced first. Here are the first two of those lemmas: $$\begin{...
57 votes
18 answers
2k views

Where and how did computers help prove a theorem?

The purposes of this question is to collect examples from theoretical computer science where the systematic use of computers was helpful in building a conjecture that lead to a theorem, falsifying a ...
13 votes
4 answers
4k views

Proof of Levenshtein distance

In the article Levenshtein distance Wikipedia says about the proof of invariant that: This proof fails to validate that the number placed in d[i,j] is in fact minimal; this is more difficult to ...
96 votes
9 answers
20k views

What would it mean to disprove Church-Turing thesis?

Sorry for the catchy title. I want to understand, what should one have to do to disprove the Church-Turing thesis? Somewhere I read it's mathematically impossible to do it! Why? Turing, Rosser etc ...
19 votes
3 answers
1k views

Examples of the value of proofs for algorithms

In teaching Intro. Algorithms to undergrads, one of the most difficult tasks is to motivate why they need to know how to prove things about algorithms. (For many students, at least in many US ...
7 votes
1 answer
205 views

Document references describing weaknesses for cutting planes and algebraic proof system?

Here, Fortnow says (section 4.3): Since then complexity theorists have shown similar weaknesses in a number of other proof systems including cutting planes, algebraic proof systems based on ...
16 votes
2 answers
1k views

Complexity of counting the number of edge covers of a graph

An edge cover is a subset of edges of a graph such that every vertex of the graph is adjacent to at least one edge of the cover. The following two papers say that counting edge covers is #P-complete: ...
7 votes
1 answer
412 views

Where is the quote "Informal proofs are algorithms, formal proofs are code" from?

Does anyone know the origin of the quote, Informal proofs are algorithms; formal proofs are code. Its made in Benjamin C. Pierce et al.'s Software Foundations.
29 votes
1 answer
5k views

What's the status of Babai's Graph isomorphism result?

It's been over a year since his January 2017 retraction and correction. Is there news? If not is this normal for validation to take this long? I would expect it would get plenty of attention. Has ...
13 votes
2 answers
1k views

An Interactive Proof of God's Number?

I've been learning about interactive proofs lately and I've been wondering if the whole thing was nothing more than a theoretical curiosity, or if it had any practical applications. I thought I'd ...
-1 votes
1 answer
70 views

Formally prove that the loops of this sorting algorithm will terminate [closed]

Given is the sorting algorithm Bubblesort ...
1 vote
0 answers
326 views

EXPSPACE proof and its implications

I'm dealing with the min-max regret 0-1 Integer Linear Programming problem (MMR-ILP, for short), which is formulated as below. \begin{equation} \label{eq:nip_obj} \min_{x \in \Phi} \sum_{i = 1}^n ...
3 votes
1 answer
697 views

Possible to do Complexity theory with only counting and Pigeonhole

Most of the proofs in the book Computational complexity by Barak and Arora seem to be Pigeonhole in disguise. What are some places in Complexity theory where counting and Pigeonhole was insufficient ...
10 votes
0 answers
261 views

How would proof of the Lindelöf hypothesis improve our understanding of computational complexity classes?

A recent press release from the Viterbi School of Engineering at USC discussed the proof of the Lindelöf hypothesis by Athanassios Fokas, a visiting professor from the Department of Applied ...
1 vote
0 answers
141 views

Proof of Sipser-Lautmann Theorem

I have written the following answer as an attempt to prove a variation of Sispser-Lautmann theorem, but it was rejected without any comments. I would appreciate if anyone can find the flaws in this ...
15 votes
1 answer
1k views

Examples of algorithms and proofs that seem correct, but aren't

In my intro to programming course, we're learning about the Initialization-Maintenance-Termination method of proving an algorithm does what we expect it to. But we've only had to prove that an ...
23 votes
4 answers
6k views

Proof of the pumping lemma for context-free languages using pushdown automata

The pumping lemma for regular languages can be proved by considering a finite state automaton which recognizes the language studied, picking a string with a length greater than its number of states, ...
2 votes
1 answer
468 views

Paxos made simple, invariant P2c

I am reading Leslie Lamport's Paxos Made Simple paper. Can someone explain why $P2^c$ implies $P2^b$? $P2^b$ If a proposal with value $v$ is chosen, then every higher-numbered proposal issued ...
3 votes
2 answers
713 views

Formally proving no algorithm exists [closed]

Are there standard techniques to show that no algorithms exist for given complexity constraints? For example, consider the following problem. The input is a list of items with exactly one duplicate, ...
2 votes
0 answers
216 views

Graph optimization problem with multiple objectives/constraints

Let's assume that we have a directed acyclic graph $G = (V, E)$, non-negative vertex weight functions $w_a(v)$ and $w_b(v)$, and a non-negative edge weight function $t(u,v)$. We can divide vertices in ...
4 votes
1 answer
498 views

Proof that the graph optimization problem is NP-hard

I'm trying to prove that the following optimization problem is NP-hard: Given a graph $G=(V,E)$, non-negative vertex weight functions $w(v)$ and $s(v)$, and a non-negative edge weight function $t(u,v)...
8 votes
1 answer
141 views

How to prove relations between "classes" of types?

After reading Effects as Sessions, Sessions as Effects, I was wondering how would a proof of equivalence between both take place, or even, a proof of Sessions types being a Type and Effect System. In ...
25 votes
4 answers
3k views

Proofs, Barriers and P vs NP

It is well known that any proof resolving the P vs NP question must overcome relativization, natural proofs and algebrization barriers. The following diagram partitions the "proof space" into ...
1 vote
2 answers
229 views

Are equalizers of regular functions always regular languages? (My guess is no because PCP, but...)

Edit: I originally defined a regular function as a function computable by a Mealy machine, but Denis pointed out that that was a weaker model than what I was thinking of. So to be more precise, by a "...
3 votes
0 answers
236 views

New proofs from "The Book" [closed]

The book "Proofs from The Book", referencing Erdős' notion of God's book, which contains the most beautiful proofs, was published in 1998. Are there any new proofs that should be considered for "...
14 votes
1 answer
650 views

How is the MA version of SETH proven to be false?

According to this paper, which discusses a nondeterministic extension of the Strong Exponential Time Hypothesis (SETH), "[…] Williams has recently shown related hypotheses about Merlin-Arthur ...
11 votes
2 answers
2k views

On the provability of P versus NP

First of all, my understanding on Gödel's incompleteness theorem (and formal logic in general) is very naive, also is my knowledge on theoretical computer science (meaning only one graduate course ...
1 vote
0 answers
71 views

Looking for reference proving polynomial-time bounds for A* search under specific conditions

In the textbook "Artificial Intelligence - A Modern Approach" (Russel, Norvig), it mentions that a sufficient criteria for the A* search algorithm to complete in polynomial time is for the heuristic ...
8 votes
3 answers
588 views

Would a proof assuming a physical law be considered sufficient?

I've always wondered if proofs in computer science would be considered sufficient proofs of the proposition if they needed to assume physical laws? For example, I'm wondering what would happen if ...
8 votes
1 answer
606 views

Humanifying computer-generated or computer assisted proofs

I remember reading a blog post displaying two versions of the same proof, one written by a human and the other by a machine, and asked the readers to tell which is which. Trying to google the post ...
-1 votes
1 answer
167 views

Undecidable Single Programs [closed]

So the halting problem basically states that there cannot exist any finite length algorithm for automatically verifying if other finite length algorithms terminate. But suppose I start listing out ...