# Thread: Turing Machine notation: sigma-star

1. ## Turing Machine notation: sigma-star

Just clean up a minor confusion:

Often in my notes when some alphabet is being defined I see:
Sigma* or {0, 1}*

I'm afraid I've forgotten the significance of the star. Is it powersets?

(note: the notation in my notes may not be consistent with what you learnt, or what is in wikipedia or what is in some other book - that really annoys me (just makes everything seem more arbitrary) )

thanks

2. Hi

Of course such notation depends on the author/professor, but in my courses it used to be the set of words in the considered alphabet. But that could really make sense, see how it is used.

3. Originally Posted by needlittlehelp01
Just clean up a minor confusion:

Often in my notes when some alphabet is being defined I see:
Sigma* or {0, 1}*

I'm afraid I've forgotten the significance of the star. Is it powersets?

(note: the notation in my notes may not be consistent with what you learnt, or what is in wikipedia or what is in some other book - that really annoys me (just makes everything seem more arbitrary) )

thanks
If the notation "*" is seen in the context of Turing machine or automata theory, I think your "*" refers to a Kleen star. I am not 100% sure though. For example, $\{0,1\}^*=\{\lambda, "0", "1", "01", "10", "11", "110",...\}$, where $\lambda$ is an empty string.