regular-language

Typically in our work we use regular expressions in capture or match operations. However, regular expressions can be used - manually at least - to generate legal sentences that match the regular expression. Of course, some regular expressions can match infinitely long sentences, e.g., the expression .+ . I have a problem that could be solved by using a regular expression sentence generating algorithm. In pseudocode, it would operate something like this: re = generate("foo(bar|baz)?", max_match = 100); #Don't give me more than 100 results assert re == ("foobar", "foobaz", "foo"); What algorithm

For example, in an assignment given to me, we were asked to find out if two regular expressions are equal or not. (a+b+c)* and ((ab)**c*)* My question is how is one supposed to do that? If I draw the transition graphs for both and then run a few strings through it and show that both of the TGs are able to accept it, is that a sufficient proof ? If not, how do I do it? Is there a mathematical/axiomatic approach towards this? Thanks in advance. EDIT: There is another thing that I'd like to clear which is kind of related to this question. Are the two FAs depicted in the photo below the same? i.e.

I have a large collection of regular expression that when matched call a particular http handler. Some of the older regex's are unreachable (e.g. a.c* ⊃ abc* ) and I'd like to prune them. Is there a library that given two regex's will tell me if the second is subset of the first? I wasn't sure this was decidable at first (it smelled like the halting problem by a different name). But it turns out it's decidable . Kevin Stricker Trying to find the complexity of this problem lead me to this paper. The formal definition of the problem can be found within: this is generally called the inclusion

I have troubles in solving/proving this problem. Any ideas please? Grijesh Chauhan L = {a n b m | n > m} is not regular language. Yes, the problem is tricky at first few try and deserve vote-up. Pumping Lemma a necessary property of regular language is tool for formal proof that language is not regular language. Formal definition: Pumping lemma for regular languages Let L be a regular language. Then there exists an integer p ≥ 1 depending only on L such that every string w in L of length at least p ( p is called the "pumping length") can be written as w = xyz (i.e., w can be divided into three

Using pumping lemma, we can easily prove that the language L1 = {WcW^R|W ∈ {a,b}*} is not a regular language . (the alphabet is {a,b,c}; W^R represents the reverse string W) However, If we replace character c with "x"(x ∈ {a,b}+) , say, L2 = {WxW^R| x, W ∈ {a,b}^+} , then L2 is a regular language . Could you give me some ideas? Grijesh Chauhan If we replace character c with x where (x ∈ {a,b} + ), say, L2 = {WXW R | x, W ∈ {a,b} + }, then L2 is a regular language. Yes, L2 is Regular Language :). You can write regular expression for L2 too. Language L2 = {WXW R | x, W ∈ {a,b} + } means: string

So this is not about the pumping lemma and how it works, it's about a pre-condition. Everywhere in the net you can read, that regular languages must pass the pumping lemma, but noweher anybody talks about finite languages, which actually are a part of regular languages. So we might all aggree, that the following language is a finite language as well as it's a regular one, but it definitely does not pass the pumping lemma: L = {'abc', 'defghi'} Please, tell me if simply no one writes about it or why we're wrong - or even not. The reason that finite languages work with the pumping lemma is

I'm trying to understand the concept of languages levels (regular, context free, context sensitive, etc.). I can look this up easily, but all explanations I find are a load of symbols and talk about sets . I have two questions: Can you describe in words what a regular language is, and how the languages differ? Where do people learn to understand this stuff? As I understand it, it is formal mathematics? I had a couple of courses at uni which used it and barely anyone understood it as the tutors just assumed we knew it. Where can I learn it and why are people "expected" to know it in so many

This is the DFA i have drawn- Is it correct? I am confused because q4 state has 2 different transitions for same input symbol which violates the rule of DFA , but I can't think of any other solution. Your DFA is not correct. your DFA is completely wrong so I don't comment DFA for RE: 0(1 + 0)*0 + 1(1 + 0)*1 Language Description : if string start with 0 it should end with 0 or if string start with 1 it should end with 1 . hence two final states (state-5, state-4). state-4 : accepts 1(1 + 0)*1 state-5 : accepts 0(1 + 0)*0 state-1 : start state. DFA : EDIT : + Operator in Regular Expression (0 +

In a CS course I'm taking there is an example of a language that is not regular: {a^nb^n | n >= 0} I can understand that it is not regular since no Finite State Automaton/Machine can be written that validates and accepts this input since it lacks a memory component. (Please correct me if I'm wrong) The wikipedia entry on Regular Language also lists this example, but does not provide a (mathematical) proof why it is not regular. Can anyone enlighten me on this and provide proof for this, or point me too a good resource? cletus What you're looking for is Pumping lemma for regular languages .