Outside built-up areas, when may the horn be used to signal an overtake, and what replaces it at night except in immediate danger?

1. The horn may be used to signal an overtake outside built-up areas; at night, flashing headlights should replace the horn except in immediate danger
2. The horn may be used freely in towns at night
3. The horn is banned in all overtaking
4. Headlight flashing is banned; only the horn may be used at night