title: Passing false to an input in HDL
body: <p>I am using the HDL from the Nand2Tetris (Elements of Computing Systems) book, and whilst looking at example gate implementations online I regularly notice something along the lines of;</p>
  
  <pre><code>CHIP ExampleZeroer {
      IN a[16], sel;
      OUT out[16];
  
      PARTS:
      Mux16(a=a, b=false, sel=sel, out=out);
  }
  </code></pre>
  
  <p>In the above example <code>false</code> is never declared anywhere. I see similar examples using the apparent keyword <code>true</code> also. If <code>false</code> is some kind of pre-declared keyword or short-hand then where does the value come from, or what is it short-hand for?</p>
  
  <p>I have implemented all of my gates without using this shorthand but it bothers me that I can't understand where the value could come from.</p>