title: What is the difference between (a+b)* and (a*b*)*?
body: <p>I assume Σ = {a, b}.
  I wanna find out the RE that means Σ*
  (Σ* means the set of all possible strings over the alphabet Σ)</p>
  
  <p>I come up with below tow REs(regular expressions)</p>
  
  <pre><code>(a+b)*
  </code></pre>
  
  <pre><code>(a*b*)*
  </code></pre>
  
  <p>However, I can't decide by myself which RE is correct or both are bad.
  So, please tell me the correct answer. </p>