title: printing lines where certain columns do not match, with awk
body: <p>I have a tab separated file like this:</p>
  
  <pre><code>1       10502   C       T  
  1       10506   C       T  
  1       10567   G       A 
  ...
  </code></pre>
  
  <p>And I'm trying to print out all lines where <code>column 3 != column 4</code>, <strong>excluding</strong> the cases where <code>column 3 = C and column 4 = T</code>.</p>
  
  <p>I tried</p>
  
  <pre><code>awk '{
  if (($3 == $4) || ($3 == C &amp;&amp; $4 == T) )
          next ;
  else
          print $0; }'
  </code></pre>
  
  <p>but I'm not sure what's going wrong...</p>