title: something about elem function in a list
body: <p>I have some issues about elem function.
  The elem function can return a bool value when the list contains the specific value. eg. elem 1 [1,2,3,5] return true.</p>
  
  <p>The question is if the list is made up with string. For instance the list is ['A2','A1']. how can I use the elem function.  I used elem 'A2' ['A1','A2'] but it doesn't work.</p>