I am just curious is there any non regular language whose subset is regular?
Is there a subset of a non regular language that is regular
1
$\begingroup$
formal-languages
regular-language
-
1Sure, any finite subset of a language is regular. Or the set of palindromes in $\{a,b\}$ is irregular but the set of palindromes in one letter is regular, if you need an infinite example. – 2012-11-13
-
0@Thomas what do you mean by a set of palindromes in one letter. Can u give an example – 2012-11-13
-
0Palindromes in one letter are just any $a*$ or $b*$. Basically, any word with only one letter is a palindrome. – 2012-11-13
-
3Ouch! You've asked 21 questions, and accepted only a handful of answers. If you have received answers which have been particularly helpful, please take the time to show appreciation by accepting such answers. – 2012-11-13
-
0I can provide a [cheat sheet](https://dl.dropbox.com/u/31345439/Theo1.jpg) from my "Theoretical Computer Science" course (in German). Just have a look at the top picture with all the boxes. From top to bottom (on thr right hand side) the descriptions are: all languages $\Sigma^*$, semi-decidable (Type 0), decidable, LOOP-decidable, NP, P, context free (Type 2), regular (Type 3), finite. Hope this might help :) – 2012-11-13
-
0@ChristianIvicevic the cheat sheet link 404'ed for me. Would you mind relinking? – 2015-09-13
-
0@piperchester This comment is very old and it seems I deleted the file from my Dropbox - luckily I have an updated version. You will find the mentioned overview of languages on the last page of my [cheatsheet](http://www.christian-ivicevic.com/Files/Theo15/Cheatsheet.pdf). – 2015-09-23