title: Flatten a list using only the forms in "The Little Schemer"
body: <p>I'm going through The LIttle Schemer to learn Scheme (as an old C programmer) and as an exercise I tried to write a procedure to flatten a list using <em>only</em> the forms in The Little Schemer;  I.e., <code>define</code>, <code>lambda</code>, <code>cond</code>, <code>car</code>, <code>cdr</code>, <code>and</code>, <code>or</code>, etc., but <em>not</em> <code>append</code>.  I thought it would be easy but I haven't been able to come up with a solution.  How can I do this ?</p>