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1500 questions
14
votes
4 answers
Star free language vs. regular language
I was wondering, since $a^*$ is itself a star-free language, is there a regular language that is not a star-free language? Could you give an example?
(from wikipdia) Lawson defines star-free languages as:
A regular language is said to be star-free…
Untitled
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What is the purpose of M:N (Hybrid) threading?
In other words, what advantages does Hybrid threading have over 1:1 (kernel only) and N:1 (user only) threading?
This is a follow-up to What is the difference between user-level threads and kernel-level threads?
Sheldon
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14
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Confluence proof for a simple rewriting system
Assume we have a simple language that consists of the terms:
$\mathtt{true}$
$\mathtt{false}$
if $t_1,t_2,t_3$ are terms then so is $\mathtt{if}\: t_1 \:\mathtt{then}\: t_2 \:\mathtt{else}\: t_3$
Now assume the following logical evaluation…
codd
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14
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5 answers
Flaw in my NP = CoNP Proof?
I have this very simple "proof" for NP = CoNP and I think I did something wrongly somewhere, but I cannot find what is wrong. Can someone help me out?
Let A be some problem in NP, and let M be the decider for A. Let B be the complement, i.e. B is in…
simpleton
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14
votes
3 answers
The importance of normal forms like Chomsky normal form for CFGs
I understand that context-free grammars can be used to represent context-free languages.It might have ambiguities. We also have normal forms like Chomsky and Greibach normal form. I couldn't understand the need of that.
Why they are important in…
user5507
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14
votes
2 answers
How many pairs of brackets are sufficient to make Brainfuck Turing complete?
Brainfuck is a Turing complete programming language that uses only 8 symbols (6 if you ignore I/O).
The two most notable ones that push it to Turing completeness are [and ], essentially Brainfuck's label and goto.
Normally, programs in Brainfuck use…
MilkyWay90
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13
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1 answer
What is the real advantage of Google's new Fuchsia operating system kernel?
Google's new in-production OS which it desires to replace not only Android but many other devices utilizes a completely new kernel:
The code differs from Android and Chrome OS due to its being based on the "Zircon" kernel (formerly "Magenta")…
Zhro
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13
votes
3 answers
P, NP and specialised Turing Machines
I'm sort of new, but very interested to the field of computing and complexity theory, and I want to clarify my understanding about how to class problems, and how strongly the problems relate to the machine being used to solve them.
My…
Bingo
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13
votes
2 answers
An example of something you can formally verify with proofs in Software Development
I have been working on understanding formal verification of software. Formal methods include things like modeling your software with Petri Nets, Automata, or State-Transition Graphs. Other techniques for formal verification include using type…
Lance Pollard
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13
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4 answers
Finding a source of a directed acyclic graph in linear time
Given a directed acyclic graph $D = (V,A)$, a vertex $v \in V$ is a source if its indegree is zero, meaning that it has only outgoing arcs.
Does there exist a linear time algorithm to find a source in a given directed acyclic graph?
Follow-up…
breezeintopl
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13
votes
2 answers
Why are CFLs not closed under intersection?
I'm struggling with understanding how context free languages can be closed under union but are not closed under intersection. I was wondering if there was a simple proof or example demonstrating that CFLs are not closed under intersection.
Zachary Galica
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13
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3 answers
Why is using a lexer/parser on binary data so wrong?
I often work with lexer/parsers, as opposed to a parser combinator and see people who never took a class in parsing, ask about parsing binary data. Typically the data is not only binary but also context sensitive. This basically leads to having only…
Guy Coder
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13
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5 answers
Why does soundness imply consistency?
I was reading the question Consistency and completeness imply soundness? and the first statement in it says:
I understand that soundness implies consistency.
Which I was quite puzzled about because I thought soundness was a weaker statement than…
Charlie Parker
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13
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Is smn theorem the same concept as currying?
I am studying the s-m-n theorem and the concept reminded me of currying.
From wikipedia article about s-m-n theorem:
the theorem says that for a given programming language and positive integers m and n, there exists a particular algorithm that…
emanek
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13
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4 answers
How does a nondeterministic Turing machine work?
What is differences between deterministic and nondeterministic Turing machines? Different but equivalent models of NDTM. In particular, what is this frequently used phrase "nondeterministically guess"? How to use it right, and examples of wrong…
fade2black
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