The tag has no wiki summary.

learn more… | top users | synonyms

3
votes
1answer
331 views

Notation of cross entropy

I have a question regarding a notation that seems to be very usual. For starters, cross entropy is defined by: \begin{align}H(X, q) &= H(X) + D(p||q) \\ & =-\sum_x p(x)\log_2 q(x)\end{align} ...
2
votes
1answer
79 views

Pumping Lemma for regular languages proof template

http://www.cs.uiuc.edu/class/fa06/cs273/Lectures/pumping-lemma/pumping-lemma.html So, I went to that site and it says: $w = xyz$ $|xy| \leq p$ $|y| \geq 1$ for all $i$, $xy^iz$ is in ...
1
vote
1answer
51 views

Proving languages are undecidable

Let L5 be the language { {G,D} | G is a CFG, D is a DFA, and L(D) ⊆ L(G) } Show that L5 is undecidable. Is L5 R.E.? Is it co-R.E.? I am not quite sure where exactly to start with this. Could ...
1
vote
1answer
24 views

Equivalence classes in a regular language

Question: Let L be a regular language, ~${_L}$ is it's equivalence relation (as was defined in Myhill Nerode theorem) that divides $\Sigma^* $ to 4 non empty equivalence classes A1, A2,A3,A4. Let ...
1
vote
1answer
52 views

How to prove that a language `L` is not a regular language?

Given the following question: Prove that the following language is not a regular language: A language L in alphabet $\Sigma = \{a, b\}$ where every word ...
1
vote
1answer
40 views

Regular language that has a string that cannot be pumped.

This is a question from a past exam. Consider the language $F = \{w | w \in 0^{*}1^{*}\}$ that is kown to be regular. a) Show that if string $w$ is chosen to be $0^p1^p$, that is a member ...
1
vote
1answer
365 views

Complement of a regular expression?

What is the regex for the complement of $r = b^*(ab + a^* + abb(b^+))^*$ ? I am thinking $(a+b)^*(abb)^+a^* $ since anything that contains $abb$ and is not followed by $b$'s would not be accepted ...
1
vote
1answer
71 views

Complement of a Set of Strings in a Language

Suppose $B= \{ 0^n1^m2^{n-m}:\, n\ge m\ge 0 \}$ Is the complement $\overline B = \{ 0^n1^m:\, 0\le n\lt m\}$? Or is it the universe of all possible strings (including all strings with symbols ...
1
vote
1answer
61 views

Working with the word w⋅y, while given the word y⋅w

$L$ is a regular language. I am given $F(L)$ such that $$F(L)= \{wy \mid yw\in L\}$$ I need to prove that if $L$ belongs to $L_\text{dfa}$, $F(L)$ also belongs to $L_\text{dfa}$. I am having a hard ...
1
vote
1answer
32 views

Regular languages that are stutter-invariant but not star-free (LTL/FO-definable)

I am looking for simple examples and/or general ideas on regular languages (I am interested in finite words and infinite words alike) that are stutter-invariant (a language $L$ over an alphabet $A$ is ...
0
votes
1answer
58 views

Is this a regular language ? SubString(L1, L2) = {w | ∃x, y ∈ L1, xwy ∈ L2}

Question: Define the following operation: SubString(L1, L2) = {w | ∃x, y ∈ L1, xwy ∈ L2} Let L1 be any language, and L2 regular. Prove that SubString(L1, L2) is regular. Thoughts: I need to somehow ...
0
votes
1answer
25 views

How to construct a context free grammar that generate following language. $\{a^nb^nc^k \in \{a,b,c\}^* | n,k >= 0\} $

$$\{a^nb^nc^k \in \{a,b,c\}^* | n,k >= 0\} $$ $E \to aEbS $ $S \to c$ I do not know where to go next, or even if this is right at all?
0
votes
1answer
63 views

How to prove that $ \{ 0^n 1^{5n} : n \ge 10000 \} $ is not a regular language?

I proved that $$ \{0^n 1^{5n} : n \ge 0\} $$ is not a regular language using Pumping Lemma by following way. Solve by contradiction that $ L = \{ 0^n 1^{5n} : n >= 0 \}$ is regular language. ...
0
votes
1answer
49 views

Question about formal languages, quotient operator L1/L2.

I come across this problem: Consider the following regular languages: L1={a*b*c*} over the alphabet A={a,b,c} L2={( a b | b b | a )*} the alphabet is the same as above. Find the shortest strings ...
0
votes
1answer
28 views

Proving non-regularity of a language

How can I prove $L = (01^n2^n | n\geq 0)$ is not regular? Would it be sufficient to say that $01^p2^p$ is in $L$ and by pumping lemma, $01^p2^p$ can be written as $xyz$ such that $|y|>0, ...
0
votes
1answer
20 views

converting to regular expression

{w | w can be written as $0^k l 0^k$ for some $k \geq 1$ and for any $l$ in ${0,1}*}$ i.e. 00010111000 can be written as 0^3 10111 0^3 How can I convert this description into a regular expression? ...
0
votes
1answer
26 views

find a regular expression

find a regular expression for w such that it does not contain $ aab $ , where w is the strings of $a$'s and $b$'s . ans: I know how to draw the same question with $ aab $ , but cant understand how to ...
0
votes
1answer
66 views

Pumping lemma proof of $L = \{a^nb^m \mid 0\leq n<m\}$

Prove the following language is not regular using the pummping lemma $L = \{a^nb^m \mid 0\leq n<m\}$ I tried solving this problem what I don't think I was able to reach an accurate proof. But this ...
3
votes
0answers
64 views

This proof in my textbook involving the pumping lemma appears incorrect - is it?

It states Let $B$ be the language $\{0^n1^n2^n | n \geq 0\}$. We use the pumping lemma to prove that $B$ is not regular. The proof is by contradiction. Assume to the contrary that $B$ is regular. ...
3
votes
0answers
83 views

Applying the Myhill-Nerode Theorem

Consider the language $$L=\{x y^{(n)} z y^{(n)} w: x,z,w \in \Sigma^*, y \in \Sigma, z\text{ does not contain }y, n \geq 0 \}.$$ To show that the language is not regular using the Myhill-Nerode ...
3
votes
0answers
824 views

Pumping lemma for $a^nb^{2n+1}$

I know how to solve pumping lemma for $a^nb^n:n\geq 0$. But I don't understand how can I solve this example : $a^nb^{2n+1}:n\geq 0$. I tried to solve it but I am not sure that I have solved it ...
2
votes
0answers
55 views

Expressiveness of finite memory programs

Assume we have a simple programming language with while, if, := (assignment), ...
2
votes
0answers
315 views

Regular, Context-free, Recursive, Recursively Enumerable Language Relationships

I am currently under the believe that all regular languages are context free, thus all regular languages are recursive, and therefore all regular languages are recursively enumerable. If I am given ...
1
vote
0answers
24 views

Why is $a^nb^n|n\geq1$ not regular and $a^nb^n|n\leq {10^{10}}$ regular?

I've heard somewhere that since the latter is bounded, it is regular. Can anyone explain me what a bound actually means? And if the latter is regular, then how would you write the regular expression ...
1
vote
0answers
30 views

Help with proving a language is regular (Sipser problem 1.49a)

I am working through Sipser's Introduction to the theory of computation on my own, so I don't have access to a teacher. Hopefully you can help me! Giving hints is highly appreciated. This question is ...
1
vote
0answers
40 views

Is this correct way to prove that { $uv$ $\mid$ $u$ and $v$ are strings over $(0,1)$ & $|u| = |v|$ } language is not regular?

I proved this using Pumping Lemma in the following way, Taking $p$ as pumping length then let us take a string $S$ where, $|u| = |v| = p$ Now according to pumping lemma $S$ can be split into three ...
1
vote
0answers
27 views

Nonregular languages that satisfy the pumping lemma at different strengths

There are three versions of the pumping lemma that I've seen, each one stronger than the last (as in it fails on some non-regular languages that pass the weaker ones) The three versions are as ...
1
vote
0answers
59 views

Proving irregularity using Myhill-Nerode theorem

I'm trying to prove that the following language is irregular using the Myhill-Nerode theorem $$ L = \{ w\space\epsilon \{a,b,c\}^* | \#_b(w) > (\#_a(w) + \#_c(w))! \} $$ While it's completely ...
1
vote
0answers
57 views

Minimal DFA for a given regular expression

How can I construct a minimal DFA from the following definition? $L=\{w \in \{a,b,c\}^* $: if the second-to-last letter from w is an $a$, then the number of $c$'s $\le 1\}$ I've already made a ...
1
vote
0answers
60 views

Prove the following by using mathematical induction

If we define the alphabet such that $$ \Sigma = {\{a,b}\} $$ and let $w$ be a string over it. I'd like to prove $$ ( \operatorname{comp}(w))^R = \operatorname{comp}(w^R) $$ where $$ w^R$$ and ...
1
vote
0answers
34 views

Why every regular language is in $\text{TIME}(n)$?

How can I prove that every regular language $R$ has linear time complexity, i.e. every regular language satisfies $$R \in \text{TIME}(n)$$
1
vote
0answers
50 views

$DFA/NFA$ for $L(OPPOSITE)=\{uv:vu\in L\}$

I'm trying to prove that: $L(OPPOSITE)=\{uv:vu\in L\} \in L_{FA}$ given that: $L \in L_{FA}$ . I'm trying to construct a finite automata that accepts $L(OPPOSITE)$ in order to prove it but I got ...
1
vote
0answers
39 views

Constructing a Turing decidable machine from DFA

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. ...
1
vote
0answers
51 views

Systematic way of creating the complement of a regular grammar?

Regular languages are closed under complement. And any regular language can be generated using a regular grammar. Is there a systematic way to create the rewrite rules for the complement of a regular ...
1
vote
0answers
42 views

Regular Functional Algorithms

A language is regular if it is accepted by a read-only Turing machine. I am curious about applying this model to functional problems rather than decision problems. Definition: A functional read-only ...
1
vote
0answers
63 views

Proving that language is regular or not regular

Let $L$ be a regular language. Prove that: $L_{+--}=\left\{w: \exists_u |u|=2|w| \wedge wu\in L\right\}$ $L_{++-}=\left\{w: \exists_u 2|u|=|w| \wedge wu\in L \right\}$ ...
1
vote
0answers
87 views

Isn't the set of all literature a regular language?

Let one piece of literature be one string. Let's define our alphabet to be sufficient to represent all literature (e.g. we may need a page-turn character, etc). So, since the collection of current ...
0
votes
0answers
19 views

Conjunction and XOR of Regular Language to DFA

If you could help me with this homework it would be greatly appreciated. If we assume that $M(i)$ is the finite automaton that recognises the regular language $L(i)$ for $i = 1,2,\ldots,n$, how can I ...
0
votes
0answers
81 views

Prove that whenever L is a regular language so is HasPrefix(L)

For a language $L$ over an alphabet $\Sigma$, define the language $\operatorname{HasPrefix}(L)$ as follows: $$\operatorname{HasPrefix}(L) = \{xy\mid x,y \in\Sigma^*, x \in L, xy \in L, |y|> 0\}$$ ...
0
votes
0answers
27 views

How to explain if such a language is regular?

Could some one explain to me whether the following languages $$L_1 = \{a^nb^n\mid n\geq 0\},\;\;\;\;L_2 = \{a,b\}^*$$ are regular or not?
0
votes
0answers
18 views

Constructing a nondeterministic automaton from deterministic

Construct a nondeterministic finite-state automaton that recognizes the language generated by the regular grammar G = {V,T,S,P} where V = {0,1,S,A,B}, T = {0,1}, S is the start symbol, and the set of ...
0
votes
0answers
16 views

Origin of the stable distribution name

Mandelbrot (1963) claimed the name stable distribution comes from Paul Levy work: "...The purpose of this paper will be to present and test such a new model of price behavior in speculative markets. ...
0
votes
0answers
38 views

contradiction of pumping lemma on even palidrome language's completion

I have the language of all the words that are not even length palindromes, or more formally: $L= \{ w: \forall u\in\Sigma^*, w\ne uu^r \}$. And I need to prove that the Pumping Lemma for regular ...
0
votes
0answers
38 views

Language of Specific Grammar

I ran into this exercise in Sipser's Note on Computation Theory. Consider the following grammar $G$: $$\begin{align} S &\to aSD \;|\; bB \\ D &\to dS \;|\; a \\ B &\to bB \;|\; ...
0
votes
0answers
13 views

A name for the number system used in versioning software

Software often uses a numbering system where one "digit" increments independently of the others. For instance, the next version of Software 2.9 might be Software 3.0 or Software 2.10 or Software ...
0
votes
0answers
60 views

Pumping lemma for $a^n b^{2n}$

I have this question and i am not sure and trying to solve in both way that is through diagram and expression: Question : Prove that $a^nb^{2n}$ is not regular. contradiction: ...
0
votes
0answers
33 views

Hierarchy of hardness for the pumping lemma for regular languages.

Whenever I bring up the Pumping lemma for regular languages people often say `better to use the Myhill-Nerode theorem'. I want to make this thought rigorous. Def: A language $L$ is pumpable if there ...
0
votes
0answers
32 views

Context-free languages

Is the following language context-free? $\{ w \in \{a,b,c\}^* : (\#_a(w) - \#_b(w)) \cdot \#_c(w) = \#_b(w)$ and all c's are encountered before any a$\}$. $\#_a(w)$ = amount of a's in w Thanks in ...
0
votes
0answers
27 views

productions with identical right hand sides for different nonterminals

Can a regular grammar contain two productions with identical right hand sides? I know in context free grammars shift reduce parsers issue reduce reduce conflicts when smth like this happens. What are ...
0
votes
0answers
132 views

Chomsky Normal Form solution for a problem

Here is my attempt at CNF, Original: $$ \begin{align*} S &\to 1 A \mid O B \\ A &\to O B O \mid 1 0 \mid \epsilon \\ B &\to A 1 A \mid 0 1 \end{align*} $$ CNF: $$ \begin{align*} S ...