# The meaning of $*$ in regular expressions

I'm designing a Turing machine that decides a language denoted by a regular expression. Let's say this expression is $a^*bbc^*$. Does this machine accept the string $bb$ since $a^*$ and $c^*$ can have zero instances or more?

• Yes, $a^*bbc^*$ matches $bb$. – Yuval Filmus Oct 24 '14 at 6:25
• The meaning of * is covered in your textbook and in any online reference such as wikipedia. You're expected to do at least basic research before asking here. – David Richerby Oct 24 '14 at 8:37

Yes, the word $bb$ in the language generated by the regular expression $a^*bbc^*$, because, as you say, $a^*$ and $c^*$ generate also the empty word. So if you are building a Turing machine that accepts this language, it should also accept the string $bb$.