function mark (E) {
  E.className = "zvyraz";
}
function unmark (E) {
  E.className = "";
}
function markpozn (E) {
  E.className = "zvyraz_pozn";
}
function obarvi (E) {
  E.className = "zadanibarevne";
}
function odbarvi (E) {
  E.className = "zadani";
}