How would I find the language for the following regular expressions over the alphabet {a, b}? aUb* (ab*Uc) ab*Ubc* a*bc*Uac EDIT: Before i get downvoted like crazy, i'd appreciate it if someone ...

I have a regular expression that was the output of a computer program. It has things like (((2)|(9)))* which a human would undoubtedly write as [29]* So I'd like a program that can make simpl...

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 abo...

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 e...

Pumping Lemma is used to prove a language to be not regular. But How a language can be proved to be regular ? In particular, Let L be a language. Define half(L) to be { x | for some y such that ...

I've seen a few comments here that mention that modern regular expressions go beyond what can be represented in a regular language. How is this so? What features of modern regular expressions are ...

As the name suggests we may think that regular expressions can match regular languages only. But regular expressions we use in practice contain stuff that I am not sure it's possible to implement w...

After having read up on RE/NFA and DFA, it seems that finding a substring within a string might actually be asymptotically faster using an RE rather than a brute force O(mn) find. My reasoning is t...

Is it possible to detect if a given string is valid regular expression, using just regular expressions? Say I have some strings, that may or may not be a valid regular expressions. I'd like to hav...

I have tried, and burned my brain to understand the definition of Regular Languages in Discrete Mathematics and its Applications(Rosen) without reaching the goal of understanding why the definition...

Most UNIX regular expressions have, besides the usual **,+,?* operators a backslash operator where \1,\2,... match whatever's in the last parentheses, so for example *L=(a*)b\1* matches the (non re...

What is the regular expression for the language 0m1n where m+n is even?

This is more of a computer science question than a programming one, but I figure that this is the best place out of all the related sites to ask this. When I discovered Regular Expressions and lo...

I'm working on some homework for my compiler class and I have the following problem: Write a regular expression for all strings of a's and b's that contain an odd number of a's or an odd number of...