        <span class="co">; etc.</span>

    (<span class="kw">char-numeric?</span> c)                   <span class="co">; #t if character is a numeral</span>
                                        <span class="co">; also alphabetic, whitespace, upper-case, lower-case</span>

    (<span class="kw">char-upcase</span> c)                     <span class="co">; return upper case character</span>
    (<span class="kw">char-downcase</span> c)                   <span class="co">; return lower case character</span