Function which verifies if a string is includes in an other one in Lisp
<p>I am trying to write a function which verifies if a string is included in another one in Lisp but I cannot</p>

<p>For example :</p>

<pre><code>(string-include 'abd 'abbbe) =&gt; nil

(string-include 'ghf 'dghfd) =&gt; ghf
</code></pre>

<p>Here is my function:</p>

<pre><code>(defun string-include (string1 string2)
  (cond
    ((not string1) 0)
    ((not string2) 0)
    ((.... (string1) (string2)) (string1 (string-include string1 (cdr string2))))
    ((string-include  string1 (cdr string2)) ) )
</code></pre>