I have just started learning regular expressions and I don't have anybody around me to help me building conceptions. So I rely on online mediums. My question is whether every regular set corresponds a language.

I had a regular expression $(0+10^*)$ and I was trying to find the regular sets. My books suggests that $L=\{0, 1, 10, 100, 1000, 10000,\ldots\}$. But I was thinking why they did not consider the strings starting with $0$ and then only one $1$ and zero or more number of occurrences of $0$, like $010, 0100, 01000$ etc.

  1. Aren't these strings belong to $L$?
  2. Is this $L$ a language? (According to me, it is a language because it is the set of strings over $\{0,1\}$.

1 Answer 1


A regular language $L$, is a set over the alphabet $\Sigma$ (that is, $L\subseteq \Sigma^*$) that has a regular expression that generates it. Therefore, by definition - any language of a regular expression is a regular language.

Regarding the language in question, $01$ for example is not generated by $(0+10^*)$, since it is not $0$ and also is not generated by $10^*$ (since it doesn't start with $1$). The same goes for any string starting with $0$, and has more than one letter in it.


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