echo '<form action="Tehtava2.php" method="POST" >';
  echo "  <p><input type=\"hidden\" name=\"id\" value=\"'session_id()'\" />";
  echo "  <p><input type=\"hidden\" name=\"log\" value=\"true\"/></p>";
  echo '  <p><input type="submit" value="Log out" /></p>';
  echo '</form>';