title: two's complement, why the name "two"
body: <p>i know unsigned,two's complement, ones' complement and sign magnitude, and the difference between these, but what i'm curious about is:</p>
  
  <ol>
  <li>why it's called two's(or ones') complement, so is there a more generalize N's complement?</li>
  <li>in which way did these genius deduce such a natural way to represent negative numbers?</li>
  </ol>