Something

<?php session_start(); define('SELF', basename(__FILE__)); if (isset($_GET['wyloguj'])) {        session_destroy();        header('Location: ' . SELF);} elseif (isset($_SESSION['login'])) {        echo 'Witaj ' . $_SESSION['login'] . '<br />        <a href="' . SELF . '?wyloguj=1">Wyloguj</a> | <a href="' . SELF . '">Dalej</a>';} else {                if (isset($_POST['login'])) {                $_SESSION['login'] = $_POST['login'];                header('Location: ' . SELF);        } else {                echo '<form action="' . SELF . '" method="post">                <input name="login" type="text" /> <input type="submit" value="Zaloguj" />                </form>';        }} ?>