title: #<PACKAGE COMMON-LISP> is locked
body: <p>I am learning the Lisp programming language. I have written a simple program:</p>
  
  <pre><code>(defun abs(x)
    (cond ((&gt; x 0) x)
          ((= x 0) 0)
          ((&lt; x 0) (- x))))
  
  (print (abs 5))
  </code></pre>
  
  <p>when I compile and run this code, i get the following warning:</p>
  
  <pre><code>WARNING: DEFUN/DEFMACRO(ABS): #&lt;PACKAGE COMMON-LISP&gt; is locked
           Ignore the lock and proceed
  WARNING: DEFUN/DEFMACRO: redefining function ABS in /home/lisp/file.lisp, was defined in C
  </code></pre>
  
  <p>I didn't understand why is this warning given, what does it mean?
  can anybody explain it?</p>