    first one to <code class="code">outchan</code> (the current output channel) and to the
     second argument. The first argument must therefore have type
     <code class="code">out_channel&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;<span class="keywordsign">'</span>b&nbsp;<span class="keywordsign">-&gt;</span>&nbsp;unit</code> and the second <code class="code"><span class="keywordsign">'</span>b</code>.
     The output produced by the function is inserted in the output of
     <code class="code">f