title: how do you append list of lists without using append in scheme?
body: <p>Say you want append these list of lists and output a single list that contains all the numbers    </p>
  
  <pre><code>(append-lists (list (list 1 2) 
                      (list 4 5) 
                      (list 10 19))) =&gt;    (list 1 2 4 5 10 19) 
  </code></pre>
  
  <p>If using trivial append, i can do this, </p>
  
  <pre><code>((define (append-lists llon)
       (cond
          [(empty? llon) empty]
          [(cons? llon)  (cons (first llon)
                         (append-lists (rest llon)))]))
  </code></pre>
  
  <p>But how to get the same output without using append just by recursion? </p>