function construct_latex_document( $formula, $fontsize=12 ) {
            global $CFG;

            $formula = filter_tex_sanitize_formula($formula);

            // $fontsize don't affects to formula's size. $density can change size
            $doc =  "\\documentclass[{$fontsize}pt]{article}\n";
            $doc .= get_config('filter_tex', 'latexpreamble');
            $doc .= "\\pagestyle{empty}\n";
            $doc .= "\\begin{document}\n";
//dlnsk            $doc .= "$ {$formula} $\n";
            if (preg_match("/^[[:space:]]*\\\\begin\\{(gather|align|alignat|multline).?\\}/i",$formula)) {
               $doc .= "$formula\n";
            } else {
               $doc .= "$ {$formula} $\n";
            }
            $doc .= "\\end{document}\n";
            return $doc;
        }