// Always fix dollars in this script.
// Very useful for converting existing text for use elswhere in Moodle, such as in pages of text.
$string = stack_maths::replace_dollars($string);
// Sort out simplification.
if ('on' == $simp) {
    $simp = true;
} else {
    $simp = false;
}
// Initially simplification should be on.
if (!$vars and !$string) {
    $simp = true;
}
if ($string) {
    $options = new stack_options();
    $options->set_site_defaults();
    $options->set_option('simplify', $simp);
    $session = new stack_cas_session(null, $options);
    if ($vars) {
        $keyvals = new stack_cas_keyval($vars, $options, 0, 't');
        $session = $keyvals->get_session();
        $varerrs = $keyvals->get_errors();
    }
    if (!$varerrs) {
        $ct = new stack_cas_text($string, $session, 0, 't');
        $displaytext = $ct->get_display_castext();
        $errs = $ct->get_errors();
        $debuginfo = $ct->get_debuginfo();
    }
}
echo $OUTPUT->header();