title: Can a decrement function be implemented from these four limited functions?
body: <p>How can I implement (if possible) a decrement function <code>dec(x){x--}</code> using only:</p>
  
  <ul>
  <li>increment(x) [x++]</li>
  <li>assign(x,y) [x=y]</li>
  <li>zero(x) [x=0]</li>
  <li>loop(x) [run whatever is inside the loop x times]</li>
  </ul>
  
  <p>I cannot use for/while loops or basic operators such as <code>+,-,/</code> -- only the above four functions.</p>