title: Checking if a number is even with only using +, - and recursion
body: <p>There has to be a way to check if a number is even or odd using recursion, addition and substraction, but without using loops.</p>
  
  <p>I could only get that far (but I am still using <code>%</code>):<br>
  <code>boolean odd = (k % 2 == 1);</code></p>
  
  <p>Does anybody have an idea?</p>
  
  <p>Thanks :)</p>