How can i delete every item from list in Prolog
<p>I want to define a relation <code>del_all(X, L, L1)</code> for removing all items <code>X</code> (if any) from list <code>L</code>. </p>

<p>Sample query:</p>

<pre><code>?- del_all(a, [a,b,a,c,d,a], L1).
L1 = [b, c, d].                           % expected answer
</code></pre>