title: How do you express Boolean negation in Scheme?
body: <p>In C and C++, the <code>!</code> negates the result:</p>
  
  <pre><code>if( !( a == b ) )
  </code></pre>
  
  <p>In Scheme, I found only <code>eq?</code>. How do I say "not equal"? Or we have to explicitly say</p>
  
  <pre><code>(eq? #f (eq? expr expr))
  </code></pre>