title: concatenation & union - regular and context free languages
body: <p>Given L1 context free non regular language.
  Given L2 regular language.</p>
  
  <p>Is it possible that L1 U L2 = regular language ?
  Also, is it possible that L1*L2 = regular language ?</p>
  
  <p>I think that the 2nd one is impossible. But I'm not sure. </p>
  
  <p>Would love to see an example if one of the abovementioned statements (or both) is/are true.</p>